The effects of two beta-adrenergic receptor blocking drugs, the non-selective propranolol and the cardioselective metoprolol, on the concentrations of blood glucose, serum insulin (IRI) and growth hormone (GH) were studied in 8 healthy male volunteers both at rest and on exercise. The tablets of 160 mg of propranolol and 200 mg of metoprolol were tested against a placebo. The heart rate and systolic blood pressure were significantly lower during treatment with the active substances than with placebo. There were no significant differences between the blood glucose and serum IRI levels after the compounds and the placebo. A decreased insulin/blood glucose ratio after exercise was seen during metoprolol. The serum GH levels were of about the same magnitude after the three different treatments but the peak values were seen 30 and 40 minutes earlier after propranolol and metoprolol than after the placebo. The concentrations of the drugs in plasma did not correlate significantly with the changes in serum levels of IRI and GH in the exercise test. In the present acute test situation propranolol and metoprolol did not significantly affect glucose homeostasis and there were no apparent differences between the drugs.