Among early cortical median nerve SEPs the frontal N30 potential is known to show amplitude reduction during execution of voluntary movements and to be abnormally reduced in parkinsonian patients. However, it is not clear whether N30 abnormalities are related to the severity of motor disability in Parkinson's disease. To address this question we studied median nerve SEPs, using a 16-channel montage, in 7 patients chronically treated with subcutaneous (s.c.) injections of apomorphine hydrochloride for spontaneous "on-off" motor fluctuations. We observed no significant changes in the latency, amplitude or scalp topography of early SEPs when comparing traces and maps obtained in the "off" condition and during the "on" phase induced by s.c. injection of apomorphine. The absence of any SEP changes, despite a clear-cut relief of the akinetic-rigid syndrome, suggests that early cortical SEPs, and in particular the frontal N30 potential, at least when recorded in a subject at rest, are not usable as an objective means to assess the severity or the fluctuations of motor disability in Parkinson's disease.