As part of our study of visual functions in age-related maculopathy (ARM) we tested reaction times to red lights of the same size and chromaticity as traffic signals. We tested under photopic and mesopic conditions with both central fixation and fixation at 5 degrees eccentricity. We examined four groups of subjects--two with normal vision, one young and the other elderly, one group of subjects with definite ARM, and another group of subjects with ophthalmoscopically visible macular changes but clinically normal visual functions, denoted preARM (PARM). There were significant differences between each of the groups tested. The ARM group showed greatly prolonged reaction time compared to the elderly normal subjects, whereas the preARM group had results between these two groups. The results indicate that functional changes are present before ARM can be diagnosed by conventional means; the consequences of these changes for the elderly motorist are discussed.