Spinal nerve stimulation in the diagnosis of lumbosacral radiculopathy. Direct spinal nerve stimulation was compared with needle electromyography (EMG) in 40 patients who were suspected of having an L5 or S1 radiculopathy. For spinal nerve stimulation, we adapted a monopolar needle electrode inserted deep into the paraspinal muscle. The minimal latency, amplitude, and negative phase area of compound muscle action potential from myotomal muscles were recorded with computer assistance. Abnormality was considered to be significant when the value fell outside of 2 SD of control mean values. Among 17 patients with clinical evidence of radiculopathy, needle EMG was abnormal in 10 patients (58.8%), whereas in the nerve stimulation test the abnormalities were shown in 16 patients (94.1%); in amplitude difference and the abnormal area, differences were shown in 12 patients (70.6%). Among 23 patients with only subjective symptoms of radiculopathy, needle EMG was abnormal in nine patients (39.1%), whereas the abnormal amplitude differences were shown in 18 patients (78.3%) and 15 patients (65.2%) with abnormal area difference by spinal nerve stimulation, respectively. Direct spinal nerve stimulation is recognized as an objective and sensitive test in the diagnosis of lumbosacral radiculopathy. 