The authors report the results of recording EVP obtained by pattern reversal in 20 controls and 43 patients with "established", "probable" or "possible" MS on the basis of MacAlpine's criteria. Whilst the latency of the wave 1 of the EVP appeared stable in the controls (107.5 msec +/- 7.46), lengthening of the latency of the EVP was seen in 77p. 100 of cases, confirming involvement of the visual pathways, though bulbar neuritis had been known clinically in only 28 p. 100 of patients. The value of this method of recording EVP in contributing to the diagnosis of DS is discussed.