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The seasonality of depressed mood was examined in 70 men and women who spent the 1991 austral winter at three American research stations in Antarctica. Seasonal Pattern Assessment Questionnaire global seasonality scores increased significantly from late summer (February/March) to midwinter (July/August; p <.001). Only one case of seasonal affective disorder (SAD) was found during midwinter, but the prevalence of subsyndromal SAD increased significantly, from 10.5 to 28.4 per 100, during this period. Station latitude was significantly associated with SAD-specific symptoms and global Structured Interview Guide for the Hamilton Depression Rating Scale-Seasonal Affective Disorders Version scores in midwinter and in early spring (October). The results suggest that even clinically normal individuals are likely to experience symptoms of subsyndromal SAD in high latitude environments, that these variations become more pronounced with increasing latitude, and that they can be detected through repeated administrations of instruments such as the Seasonal Pattern Assessment Questionnaire and Structured Interview Guide for the Hamilton Depression Rating Scale-Seasonal Affective Disorders Version.