Conduction in central motor pathways and motor roots was assessed, using the new technique of magnetic stimulation, in 39 patients with cervical spondylosis. Recordings were taken from abductor digiti minimi in all patients and from biceps brachii and abductor hallucis in some. Findings were abnormal ipsilaterally in 27 out of 63 muscles examined in patients with myelopathy, and in 2 out of 38 muscles in patients with radiculopathy. No abnormality was found in 11 muscles examined in patients with negative radiology. There was some correlation between the degree of electrophysiological change and clinical disability. Abnormal conduction was found in some patients with cord compression at the C3/4 or C4/5 interspace but not in a small group with compression at the C5/6 interspace. It seems that magnetic stimulation will provide objective confirmation of upper motor neurone involvement and may provide some measure of its degree, but at present it does not appear to be superior to clinical methods in diagnosing its presence. It may also aid the selection of the correct level for surgical decompression.