An electrophysiological study was made of 30 normal subjects aged 20 to 70 years. Routine methods were used to measure peripheral motor and sensory functions of the posterior tibial nerve. This nerve was then stimulated at the ankle and recordings made simultaneously over the thoraco-lumbar spine, cervical spine and central sensory cortex. Peripheral and central potentials were reproducibly recorded at each site in all subjects. Peripheral nerve motor and sensory potential amplitudes fell significantly with age, as did the amplitude of the thoraco-lumbar potential. Cervical and central potential amplitudes did not change significantly with age. The peak latencies of thoraco-lumbar, cervical and central potentials all showed a significant increase with age. In addition, when 'central conduction time' was calculated by subtracting thoraco-lumbar or cervical latency from the latency of the cortical potential, a significant prolongation with increasing age was still seen, especially in more rostral pathways.