Nine female subjects with anorexia nervosa (AN) were studied when emaciated (mean 72% of average body weight), and after refeeding (mean 85% of average body weight). They were compared to 9 individually age-matched female control subjects. On each occasion blood was sampled for serum melatonin and plasma cortisol through the night, and urine was collected over 24 hr to measure sulfatoxy melatonin levels. The AN group did not differ in their level of depression before and after weight gain. There were no significant differences in serum melatonin values among the patient group before or after weight gain and the control group. Levels of urinary sulfatoxy melatonin were also significantly higher in nighttime compared to daytime samples both before and after weight gain. Plasma cortisol values were significantly elevated in the emaciated state and this was accounted for by higher cortisol levels at 9, 10, 11, and 12 PM and at 6 AM compared with the weight restored state and to controls. This study suggests that pineal activity in patients with AN is not altered by chronic changes in weight, and is not closely associated with changes in cortisol.