We used 31P NMR spectroscopy to study the effect of acebutolol on the metabolic disturbances caused by ischaemia in the isolated rat heart. The intracellular acidosis and high-energy phosphate compound depletion induced by global low-flow ischaemia were significantly attenuated in the presence of acebutolol 2.7 X 10(-5) and 1.35 X 10(-4) M. The drug displayed no significant effect either at the 5.4 X 10(-6) M concentration or when administered as pretreatment to the animals (50 mg X kg-1, 120 and 60 min before isolating the heart). Since acebutolol had no effect on the contractility of the isolated rat heart at the 2.7 X 10(-5) M concentration the present results suggest that the mechanisms through which acebutolol exerts its effects on energy metabolism are not related to a reduction of cardiac work. The possible contribution of the membrane-stabilizing property of the drug is suggested by the fact that high concentrations are needed and that a short pretreatment had no effect.