The effects of 1 night of total sleep deprivation on mood state and visual light-dark adaptation were studied in 15 patients with major depression and nine normal comparison subjects. Mood improvements were evident in all but one patient, although responders (n = 9) could be easily distinguished from nonresponders (n = 6). No significant group differences were found in ocular responses before treatment. After treatment, however, light-adapted peak corneofundal potentials increased in patient responders and decreased in patient nonresponders and normal subjects. Moreover, changes in peak values were closely correlated (r = -0.74) with changes in scores on the Hamilton Depression Rating Scale. In contrast, dark-adapted trough potentials did not distinguish between diagnostic groups and were not correlated with clinical responses. The results indicate that sleep deprivation induces changes in light sensitivity that are proportional to improvements in depressive state.