Eleven patients suffering from chronic progressive external ophthalmoplegia (CPEO) were investigated by means of electroretinograms (ERG) and visually evoked cortical potentials (VECP) to flash and checkerboard-reversal stimuli. One patient exhibited a Kearns syndrome, in two patients fundoscopy revealed pigmentary retinopathy, and the other eight patients had normal fundi. In the three patients with pigmentary retinopathy the ERGs were slightly disturbed or normal, the P100-latencies in the VECPs being normal. Three out of eight patients without pigmentary changes had reduced ERGs indicating unsuspected retinopathy. This nonpigmentary retinopathy was only detected by means of ERG and may be the electrophysiological correlate of a reduced visual acuity. One patient had a considerably prolonged P100-latency in the pattern-reversal VECP of one eye, which may indicate lesions of the visual pathway along with CPEO.