XH-40: The initial Bell 204 prototype.
Three prototypes were built, equipped with the Lycoming XT-53-L-1 engine of 700 shp (520 kW).

YH-40: Six aircraft for evaluation, as XH-40 with 12-inch (300 mm) cabin stretch and other modifications.

Bell Model 533: One YH-40BF rebuilt as a flight test bed with turbojet engines and wings.

HU-1A: Initial Bell 204 production model, redesignated as the UH-1A in 1962.
182 built.

TH-1A: UH-1A with dual controls and blind-flying instruments, 14 conversions.

XH-1A: A single UH-1A was redesignated for grenade launcher testing in 1960.

HU-1B: Upgraded HU-1A, various external and rotor improvements.
Redesignated UH-1B in 1962.
1014 built plus four prototypes designated YUH-1B.
NUH-1B: a single test aircraft, serial number 64–18261.

UH-1C: The UH-1B gunship lacked the power necessary to carry weapons and ammunition and keep up with transport Hueys, and so Bell designed yet another Huey variant, the "UH-1C", intended strictly for the gunship role.
It is an UH-1B with improved engine, modified blades and rotor-head for better performance in the gunship role.
767 built.

YUH-1D: Seven pre-production prototypes of the UH-1D.
UH-1D: Initial Bell 205 production model (long fuselage version of the 204).
 Designed as a troop carrier to replace the CH-34 then in US Army service.
2008 built many later converted to UH-1H standard.

HH-1D: Army crash rescue variant of UH-1D.
UH-1E: UH-1B/C for USMC with different avionics and equipment.
192 built.

NUH-1E: UH-1E configured for testing.

TH-1E: UH-1C configured for Marine Corps training.
Twenty were built in 1965.

UH-1F: UH-1B/C for USAF with General Electric T58-GE-3 engine of 1,325 shp (988 kW).
120 built.

TH-1F: Instrument and Rescue Trainer based on the UH-1F for the USAF.
26 built.

UH-1H: Improved UH-1D with a Lycoming T53-L-13 engine of 1,400 shp (1,000 kW).
5435 built.

CUH-1H: Canadian Forces designation for the UH-1H utility transport helicopter.
Redesignated CH-118.
A total of 10 built.

EH-1H: Twenty-two aircraft converted by installation of AN/ARQ-33 radio intercept and jamming equipment for Project Quick Fix.

HH-1H: SAR variant for the USAF with rescue hoist.
A total of 30 built.

JUH-1: Five UH-1Hs converted to SOTAS battlefield surveillance configuration with belly-mounted airborne radar.

TH-1H: Recently modified UH-1Hs for use as basic helicopter flight trainers by the USAF.

HH-1K: Purpose built SAR variant of the Model 204 for the US Navy with USN avionics and equipment.
27 built.

TH-1L: Helicopter flight trainer based on the HH-1K for the USN.
A total of 45 were built.

UH-1L: Utility variant of the TH-1L. Eight were built.

UH-1M: Gunship specific UH-1C upgrade with Lycoming T53-L-13 engine of 1,400 shp (1,000 kW).

UH-1N: Initial Bell 212 production model, the Bell "Twin Pac" twin-engined Huey powered by Pratt & Whitney Canada T400-CP-400.

UH-1P: UH-1F variant for USAF for special operations use and attack operations used solely by the USAF 20th Special Operations Squadron, "the Green Hornets".

EH-1U: No more than 2 UH-1H aircraft modified for Multiple Target Electronic Warfare System (MULTEWS).

UH-1V: Aeromedical evacuation, rescue version for the US Army.

EH-1X: Ten Electronic warfare UH-1Hs converted under "Quick Fix IIA".

UH-1Y: Upgraded variant developed from existing upgraded late model UH-1Ns, with additional emphasis on commonality with the AH-1Z.
Note: In U.S. service the G, J, Q, R, S, T, W and Z model designations are used by the AH-1.
 The UH-1 and AH-1 are considered members of the same H-1 series.
The military does not use I (India) or O (Oscar) for aircraft designations to avoid confusion with "one" and "zero" respectively.
XH-40: The initial Bell 204 prototype. Three prototypes were built, equipped with the Lycoming XT-53-L-1 engine of 700 shp (520 kW).
YH-40: Six aircraft for evaluation, as XH-40 with 12-inch (300 mm) cabin stretch and other modifications.
Bell Model 533: One YH-40BF rebuilt as a flight test bed with turbojet engines and wings.
HU-1A: Initial Bell 204 production model, redesignated as the UH-1A in 1962. 182 built.
TH-1A: UH-1A with dual controls and blind-flying instruments, 14 conversions.
XH-1A: A single UH-1A was redesignated for grenade launcher testing in 1960.
HU-1B: Upgraded HU-1A, various external and rotor improvements. Redesignated UH-1B in 1962. 1014 built plus four prototypes designated YUH-1B.
NUH-1B: a single test aircraft, serial number 64–18261.
UH-1C: The UH-1B gunship lacked the power necessary to carry weapons and ammunition and keep up with transport Hueys, and so Bell designed yet another Huey variant, the "UH-1C", intended strictly for the gunship role. It is an UH-1B with improved engine, modified blades and rotor-head for better performance in the gunship role. 767 built.
YUH-1D: Seven pre-production prototypes of the UH-1D.
UH-1D: Initial Bell 205 production model (long fuselage version of the 204).  Designed as a troop carrier to replace the CH-34 then in US Army service. 2008 built many later converted to UH-1H standard.
HH-1D: Army crash rescue variant of UH-1D.
UH-1E: UH-1B/C for USMC with different avionics and equipment. 192 built.
NUH-1E: UH-1E configured for testing.
TH-1E: UH-1C configured for Marine Corps training. Twenty were built in 1965.
UH-1F: UH-1B/C for USAF with General Electric T58-GE-3 engine of 1,325 shp (988 kW). 120 built.
TH-1F: Instrument and Rescue Trainer based on the UH-1F for the USAF. 26 built.
UH-1H: Improved UH-1D with a Lycoming T53-L-13 engine of 1,400 shp (1,000 kW). 5435 built.
CUH-1H: Canadian Forces designation for the UH-1H utility transport helicopter. Redesignated CH-118. A total of 10 built.
EH-1H: Twenty-two aircraft converted by installation of AN/ARQ-33 radio intercept and jamming equipment for Project Quick Fix.
HH-1H: SAR variant for the USAF with rescue hoist. A total of 30 built.
JUH-1: Five UH-1Hs converted to SOTAS battlefield surveillance configuration with belly-mounted airborne radar.
TH-1H: Recently modified UH-1Hs for use as basic helicopter flight trainers by the USAF.
HH-1K: Purpose built SAR variant of the Model 204 for the US Navy with USN avionics and equipment. 27 built.
TH-1L: Helicopter flight trainer based on the HH-1K for the USN. A total of 45 were built.
UH-1L: Utility variant of the TH-1L. Eight were built.
UH-1M: Gunship specific UH-1C upgrade with Lycoming T53-L-13 engine of 1,400 shp (1,000 kW).
UH-1N: Initial Bell 212 production model, the Bell "Twin Pac" twin-engined Huey powered by Pratt & Whitney Canada T400-CP-400.
UH-1P: UH-1F variant for USAF for special operations use and attack operations used solely by the USAF 20th Special Operations Squadron, "the Green Hornets".
EH-1U: No more than 2 UH-1H aircraft modified for Multiple Target Electronic Warfare System (MULTEWS).
UH-1V: Aeromedical evacuation, rescue version for the US Army.
EH-1X: Ten Electronic warfare UH-1Hs converted under "Quick Fix IIA".
UH-1Y: Upgraded variant developed from existing upgraded late model UH-1Ns, with additional emphasis on commonality with the AH-1Z.
Note: In U.S. service the G, J, Q, R, S, T, W and Z model designations are used by the AH-1.  The UH-1 and AH-1 are considered members of the same H-1 series. The military does not use I (India) or O (Oscar) for aircraft designations to avoid confusion with "one" and "zero" respectively.
Bell UH-1 Iroquois