TRH and LHRH were simultaneously infused into a group of five male patients with primary unipolar depression and four male secondary depressed patients. Blood samples were measured for LH and TSH just before and two hours following infusion. Six healthy male subjects matched for age were similarly studied. Our results showed: 1) that basal levels of TSH and LH were not different in any of the three groups of subjects, 2) TSH responses in the three groups were not significantly different, and 3) the LH response was significantly greater in the secondary depressed patients than the primary unipolar depression and normal controls at all time intervals after infusion. Our results add to the existing evidence for an abnormality in the hypothalamo-pituitary regulation of pituitary hormones-in particular LH. Such an abnormalit has not been reported in the literature to our knowledge. Our results tend to suggest a biological difference in the two subtypes of depression studied. Neuroendocrine studies would appear to be a useful diagnostic procedure in the differentiation of these subtypes of depression.