As part of the Collaborative Study of the Psychobiology of Depression, we have examined the pretreatment growth hormone response (ΔGH) to insulin (0·1 U/kg) and the magnitude of the hypoglycaemic response in a large number of well-defined depressed patients (N = 132) and healthy controls (N = 80). After applying rigorous exclusion criteria, data were analysed from 93 patients and 66 controls for blood glucose response and from 56 patients and 52 controls for ΔGH. Depressed patients, either unipolar or bipolar, showed less of a fall in glucose than controls. A weak association was found between the magnitude of the fall in glucose and the severity of depression. No significant differences were found in values for ΔGH between the unipolar or bipolar depressed patients and controls either for males, pre-menopausal or postmenopausal females, or the total female group. These data do not support previous claims of a lowered ΔGH response to insulin in depressed patients. However, the resistance to hypoglycaemia seen in the depressed patients is consistent with previous reports.