Seasonal affective disorder is a subtype of depression characterized by depressed mood, lack of energy, hypersomnia, craving for carbohydrates, overeating, and weight gain with a pattern of seasonal change (1). A more prevalent but attenuated form of the disorder has been labeled "subsyndromal seasonal affective disorder." Although the effect of the seasons on mood has been mentioned throughout the ages, light and its effect on seasonal variations in mood have been subjected to much more intense study since the early 1980s. An increased focus on exploration of circadian rhythms, along with the discovery of the effectiveness of bright light treatment and its subsequent commercial availability, has augmented the international study of this disorder. The syndrome is often explored in the popular press, leading to substantial public awareness. Perhaps some of the interest is due to the fact that there is anecdotal as well as research evidence that seasonal variations in mood may be present in the normal population.