GH secretion is markedly altered in diabetic rats and humans. Diabetes in the rat, whether occurring spontaneously or after streptozotocin administration, results in depressed GH secretion. This defect is likely caused by an increase in hypothalamic somatostatin tone and decreased pituitary GH. The effects of diabetes in humans depend upon the etiology of the disease. In type-1 diabetes, GH secretion is increased and in type 2 it is decreased. Again, these changes are hypothesized to be due to opposite alterations in hypothalamic somatostatin. Current evidence suggests that GH hypersecretion in human type-1 diabetes may be relevant to important metabolic and angiopathic complications of the disease.