A factorial design was applied in this multicenter, double-blind, placebo-controlled trial of the calcium-channel blocker verapamil and the ACE inhibitor enalapril to assess the hypotensive effects of the combination compared with monotherapy, to evaluate safety, and to determine the effects on quality of life (QOL) of both drugs, alone and in combination. The study consisted of a 3 x 2 factorial design wherein 186 men and women with a sitting diastolic blood pressure (BP) of between 95 mm Hg and 114 mm Hg, after a 4-week placebo washout, were randomized to one of six treatment groups for 4 weeks of active treatment. Monotherapy with both 240 mg verapamil and 10 mg enalapril reduced systolic and diastolic BP to a similar extent and significantly more than placebo. The 240 mg verapamil + 10 mg enalapril combination was additive for both systolic and diastolic blood pressure; 120 mg verapamil + 10 mg enalapril was additive for systolic BP only. The total number of adverse events reported was similar for all six treatment groups. QOL scores were unchanged from baseline and not different between treatment groups. The combination of 240 mg verapamil and 10 mg enalapril was significantly more effective at reducing BP than either drug alone; this additivity of effect was not linked to a higher rate of adverse experiences or to a deterioration in QOL. Thus, combination therapy at lower doses may offer an alternative treatment option to higher dose monotherapy.