1. The following four intravenous treatments were administered in a balanced, randomized, Latin square design to four healthy volunteers: (1) saline injection (10 min); salbutamol infusion (0.15 microgram kg-1 min-1 for 60 min) (sS), (2) propranolol injection (0.3 mg kg-1 for 10 min); salbutamol infusion (pS), (3) practolol injection (2 mg kg-1 for 10 min); salbutamol infusion (PS) and (4) saline injection; saline infusion (ss). 2. Heart rate was recorded and venous blood taken for estimation of insulin, glucose and potassium before and after each injection (0 and 12-15 min) and at various times during the infusion (30,45,60 and 75 min). 3. The mean, peak % heart rate changes from baseline, control were +65.8%, +23.0%, -10.9% and -12.1%, the mean, peak % glucose changes, +61.0%, +7.1%, +3.6% and +6.9%, and the mean, peak % insulin changes, +298%, +28%, -28% and -43% during the infusions for sS, PS, ss and pS respectively. 4. The mean serum potassium levels before the injections and at the completion of the infusions were 3.98 and 3.08 4.03 and 3.63, 4.07 and 4.15, and 4.03 and 4.13 meq/l for sS, PS, ss and pS respectively. 5. Propanolol completely abolished the cardiac and metabolic responses of salbutamol. 6. Practolol produced only partial cardiac beta-adrenoceptor blockade, but completely inhibited the metabolic actions of salbutamol.