Foveal cone electroretinograms (ERGs) were recorded in five patients (aged 24 to 66 years) referred because of central visual loss of unexplained etiology. These patients had no family history of visual loss and no diagnostic fundus abnormalities seen on ophthalmoscopy or fluorescein angiography. Foveal cone ERGs were elicited with a 4 degrees white stimulus flickering at 42 Hz centered within a steady 10 degrees white surround presented through the dilated pupil to the fovea by a hand-held, dual-beam stimulator-ophthalmoscope. All five patients showed reduced foveal cone ERG amplitudes. Their abnormal responses were similar to those previously reported in cases of clinically apparent macular degeneration and contrasted with previously reported normal responses in patients with optic atrophy or strabismic amblyopia. The progressive loss of central vision as determined by history and these subnormal foveal cone ERG amplitudes suggest that these patients have a form of macular degeneration.