Research has supported the applicability and efficacy of light therapy in the treatment of nonseasonal depression. The investigators examined the effects of light therapy on sleep, core temperature, depressed mood, and perception of fatigue and energy in a sample of pre-menopausal and post-menopausal women diagnosed with nonseasonal, nonbipolar depression. Women were randomly assigned to either light therapy (n = 16) or placebo (n = 13) for a 28-day period. Pre and post measures of sleep and core temperature were collected. In addition, measures of depressed mood, fatigue, and energy were collected throughout the study period. Significant changes in depression and energy were found in the treatment group, but not in the placebo group. There was a significant reduction in the temperature mesor and less wake time during the first third of the sleep period in the treatment group but not in the placebo group. Light therapy yielded significant improvement in depression when compared with placebo intervention and core temperature mesor returned to normal. There was no significant phase shift, perhaps due in part to the absence of any baseline circadian phase disturbances. Relationships between temperature, sleep, depressed mood, fatigue, and energy variables offer potential directions for future research and clinical intervention.