Focal cone electroretinograms were obtained with a 3-degree flickering stimulus from 100 normal eyes and 134 eyes with known macular disease. Responses were obtained during direct visualization of the fundus with a hand-held stimulator-ophthalmoscope. Mean foveal cone amplitude for 100 normal eyes was 0.31 microV, with 95% of all amplitudes greater than 0.18 microV. There was a significant inverse correlation between amplitude and age for responses obtained from the fovea (r = -0.91; p less than 0.001) but not for responses obtained from the parafovea (midway between fovea and disk, r = -0.53; not significant). In eyes with known maculopathy, mean foveal cone amplitude was correlated with Snellen acuity. Even after correcting for normal decreases in amplitude with age, responses were significantly reduced in 88/94 (94%) of all eyes with 20/40 or poorer acuity, suggesting that the focal electroretinogram is a sensitive test for detecting macular disease.