We compared the effects of diltiazem sustained-release formulation and metoprolol on diurnal ambulatory blood pressure (BP) and plasma lipoprotein levels. Forty-nine patients with primary hypertension were included in a randomized, double-blind, crossover study, and 44 completed the trial. Both diltiazem and metoprolol significantly lowered office (p less than 0.001) and diurnal ambulatory BP (p less than 0.01). After 16 weeks of therapy with diltiazem, mean ambulatory BP decreased 10/7 mm Hg, whereas metoprolol lowered BP by 16/10 mm Hg (p less than 0.001 for systolic BP and p less than 0.01 for diastolic BP). Moreover, metoprolol seemed to induce a greater reduction in morning BP at work. Although diltiazem had no effect on lipid levels, treatment with metoprolol was associated with a significant rise in triglyceride levels (p less than 0.001 vs baseline and diltiazem), total cholesterol levels (p less than 0.05 vs baseline), atherogenic index (p less than 0.05 vs baseline and diltiazem) and very low-density lipoprotein and cholesterol levels (p less than 0.001 vs baseline and diltiazem) and a significant decrease in high-density lipoprotein cholesterol levels (p less than 0.01 vs baseline and p less than 0.001 vs diltiazem). These data suggest that both diltiazem and metoprolol provide adequate office BP control. The deleterious effects of metoprolol on lipid and lipoprotein levels may counterbalance its beneficial effects on reduction of ambulatory BP.