Visual evoked responses were obtained in 47 Parkinsonian patients and 26 age-matched controls. The stimulation to binocular and uniocular latency of the major positive peak was longer in the Parkinsonian patients and its amplitude was smaller than in the control subjects. There was a large interocular difference suggesting that at least part of the delay occurs at prechiasmatic level. The latency and amplitude varied markedly following ingestion of levodopa as Sinemet. Auditory evoked potentials were obtained in 16 Parkinsonian patients and 11 age-matched controls. The latency of the NV wave was prolonged in the former although the amplitude was the same, suggesting that the abnormality may be a widespread one.