The electroretinogram (ERG) and the occipital visual evoked potential (VEP) evoked by sinusoidal grating stimuli have been recorded in cases with a past history of optic neuritis. Although a significant reduction in pattern ERG amplitude was found in the patient group there was considerable overlap between the patient and the control populations. The pattern ERG was not found to be a sensitive test in providing evidence of a previous attack of optic neuritis. Reduction in VEP amplitude was considerably greater than was the reduction in ERG amplitude. The residual visual deficit in the patients was quantified by measuring contrast sensitivity. Overall, the greater the residual deficit the greater was the ERG abnormality, but in some individual patients it was found that the contrast sensitivity loss and the ERG amplitude reduction were not well correlated. No evidence was found for a latency change peripheral to the generators of the pattern ERG which might contribute to the VEP latency changes which occur following an attack of optic neuritis.