Metoprolol is a beta1-selective adrenoceptor blocking drug. In hypertension, its duration of effect is longer than expected from its half-life and it is suitable for twice daily administration. There is some evidence that once daily administration may be possible in treating hypertension. It is similar in efficacy to other beta-adrenoceptor blocking drugs in angina pectoris and essential hypertension, when given in equiactive beta-blocking dosages. Metoprolol is well tolerated and side-effects have not proved a problem. It has some pharmacodynamic and pharmacokinetic differences from other beta-adrenoceptor blocking drugs and may prove useful in cases where these differences are shown to be clinically important.