Sleep onset is a powerful physiologic stimulus for growth hormone secretion. Difficulty falling asleep and poor sleep maintenance are prominent symptoms in patients with a major depressive disorder. Much of the disturbance in the sleep electroencephalograms of depressed patients occurs within the first half of the night, the time when growth hormone is usually secreted. Growth hormone secretion was measured during electroencephalographically monitored sleep in 38 patients with a recurrent major depressive disorder and 35 healthy control subjects. Before treatment, depressed patients had a statistically significant reduction in growth hormone secretion during sleep. This reduction, which persisted through treatment and recovery into the drug-free remitted state, may be a trait marker in patients with a recurrent depressive disorder.