Muscle responses evoked on transcranial stimulation of the motor cortex (corticomotor) and motor roots (spinal) were studied in 20 healthy volunteers using a simplification of Rossini's technique and conventional EMG equipment. Cortical motor responses were consistently obtained from the contralateral upper limb with tolerable stimuli. Lower limb motor responses were inconsistent and sometimes required uncomfortably high stimulus strengths. In the upper limbs, peripheral conduction time (PCT) was estimated by the latency of the response to spinal stimulation. A comparable measure of PCT was obtained for the abductor pollicis brevis (APB) from the F-responses. The difference between the latency of the corticomotor response and the PCT was considered to represent central motor conduction time (CMCT). Corticomotor latencies were: APB 18.51 +/- 1.1 msec, biceps 9.77 +/- 0.46 msec and tibialis anterior 26.5 +/- 2.9 msec. CMCT from cortex to C8/T1 segments (APB) was 4.68 +/- 0.6 msec and between cortex and C5/C6 (biceps) 4.24 +/- 0.42 msec.