['To determine if the antidepressant effect of 1 hour of light therapy is predictive of the response after 1 and 2 weeks of treatment in patients with seasonal affective disorder (SAD).', 'Twelve patients with SAD.', 'National Institutes of Health Clinical Center, Bethesda, Md.', 'Light therapy for 2 weeks.', 'Scores on the Seasonal Affective Disorder Version of the Hamilton Depression Rating Scale (SIGH-SAD) on 4 occasions (before and after 1 hour of light therapy and after 1 and 2 weeks of therapy) in the winter when the patients were depressed. Change on typical and atypical depressive scores at these time points were compared.', 'Improvement of atypical depressive symptoms after 1 hour of light therapy positively correlated with improvement after 2 weeks of therapy.'] Does early response to light therapy partially predict long-term antidepressant effects in patients with seasonal affective disorder?