To discern whether the multiple neuroendocrine-metabolic dysfunctions observed in women with anorexia nervosa (AN) and bulimia nervosa (BN) are associated with altered diurnal variations in serum melatonin profiles, we compared cycling and amenorrheic women with normal weight BN (n = 8) and AN (n = 7) to 21 normal cycling controls. Endogenous depression, which has confounded prior studies of melatonin profiles in women with eating disorders, was excluded in all subjects. Serum samples for melatonin measurements were obtained at frequent intervals (every 20 min) in a controlled light-dark environment, and cycling women were studied in the early follicular phase of the menstrual cycle. Mean (+/- SE) peak melatonin levels were similar in AN, BN, and controls (325 +/- 43, 310 +/- 33, and 334 +/- 30 pmol/L, respectively). The time of melatonin peak, the time of onset and offset of the nocturnal serum melatonin excursion, and the duration of the nocturnal elevation were also similar in the three groups. Analysis of covariance revealed no independent effects of age or time of year on the data. Moreover, when subjects were separated into those with and without menstrual cyclicity, no significant differences in any parameter of melatonin diurnal variation were observed. Taken together, these data suggest that pineal melatonin secretion is unaltered in women with eating disorders, in whom depression is excluded, and that the frequent occurrence of amenorrhea in this population is not mediated by melatonin.