A study was carried out of 32 patients suffering from multiple sclerosis the diagnois of which was quite definite according to Mac Alpine's criteria and which had developed over more than two years. Comparison was made with patient suffering from optic neuritis of a different aetiology and with normal subjects. The method of investigation was dynamic electroretinoencephalography : the visual evoked potentials were investigated after stimulation by white and coloured light before and after adapatation to darkness. The specificity of the results was tested by, firstly, electro-retinogram recording for control of the visual system, and secondly, by the recording of auditory evoked potentials for control cerebral function. Abnormalities in visual evoked potentials were found in 77 percent of the cases. In particular, there was delayed latency, that is, a slowing of retino-cortical conduction. The significance of these abnormalities is discussed, by analyzing the electroclinical correlationships according to whether there was obvious or subclinical optic neuritis, and the dissemination, activity or duration of the disease. The incidence of visual evoked potential abnormalities was considerably greater than that in optic neuritis (35 percent). The links between abnormalities in nervous conduction and demyelinisation are emphasized. The role and specificity of electrophysiological investigation in diagnosis of multiple sclerosis are discussed.