Various doses of verapamil, using the conventional and sustained release formulations, have been administered for the treatment of mild or moderate hypertension in different controlled studies for periods of 4-6 weeks, involving a total of 103 patients, and in one long-term trial for 1 year in 12 patients. A double-blind comparison of verapamil and nifedipine showed that the two calcium antagonists had equal antihypertensive action. A significant blood pressure (BP) reduction was achieved with verapamil both at rest and during isometric exercise in the great majority of patients. No significant correlation was found between age and BP reduction, but pretreatment BP and pressure reduction correlated positively. Heart rate (HR) was moderately but significantly reduced by verapamil. The established wide interindividual differences in verapamil pharmacokinetics were confirmed. There was no significant correlation between plasma drug concentrations and BP reduction, but the dosage regimens with the highest mean plasma drug concentrations were associated with the greatest mean reduction in BP. A moderate, but significant, prolongation of AV-conduction was demonstrated. QRS- and QT-intervals were unaffected. Side-effects, with all formulations of verapamil, were generally mild and often transient. No significant haematological or metabolic effects were observed during long-term treatment. It is concluded that the calcium antagonist verapamil is an effective and safe drug. It can be considered as an alternative drug in mild and moderate essential hypertension.