The mechanism responsible for the suppression of GH secretion in hyperglycaemia and hypoglycaemia in rats has been investigated using perifusion of anterior pituitary cells. When perifused with Krebs-Ringer bicarbonate containing normal (5 mmol/l), high (20 mmol/l) and low (1 mmol/l) concentrations of glucose, the GH responses to GH-releasing factor (GRF) were 85 +/- 5, 85.5 +/- 5.4 and 89 +/- 3.0 (S.E.M.)% respectively compared with the initial response to GRF at 5 mmol/l in each column. The mean GH response to GRF from anterior pituitary cells of normal rats was 6.58 +/- 0.88 micrograms/three pituitaries, which was not statistically different form that of cells from rats with streptozotocin-induced diabetes (5.40 +/- 0.68 micrograms/three pituitaries). It is concluded that GH suppression in diabetic rats and during hypoglycaemia is not mediated by changes in the GH response to GRF.