A direct compare of the diagnostic accuracy as to PD between duplex and SPECT scans has until now not been made. Our hypothesis is that the TCD of substantia nigra duplex scanning is an accurate diagnostic tool and deserves a place in the diagnostic work-up of PD/Parkinsonism patients and diagnostically efficient enough to replace 50% of SPECT scans. In comparison with SPECT duplex scanning is less costly (respectively 80 euro and 400 euro for each SPECT) and more comfortable for the patient.