Circadian secretion of melatonin was measured in melancholic depressed patients (n = 9) and age- and sex-matched healthy control patients (n = 9). The mean age of the depressed patients was 29 years, i.e. younger than in most earlier studies, and a drug-free interval of 3 weeks preceded the investigations. Melatonin secretion was similar in depressed patients and healthy subjects with no significant differences at any of the time points, thus not confirming earlier studies in which depressed patients were found to have lower melatonin levels than control patients. The discrepancy between our result and earlier studies may be explained by different patient characteristics such as age, duration of illness, previous treatment, and alcohol intake. It is conceivable that a diminution of nocturnal melatonin secretion in depressed patients might only occur during the long-term course of the depressive illness and/or its pharmacological treatment.