The objective of the study was to assess the effects of the calcium antagonist isradipine on plasma lipids, lipoproteins, and apolipoproteins in patients with essential hypertension. After a four-week placebo wash-out period, 73 patients (41 men, 32 women) were studied in a double-blind, randomized, crossover study comparing sustained-release isradipine (isradipine SR) with the standard isradipine formulation. Nineteen patients received 5 mg/day and 54 patients 10 mg/day. Lipids were evaluated at the end of the placebo period and after 12 weeks of treatment with isradipine. In both treatment groups, lipid and lipoproteins were not modified. However, apolipoprotein A-I levels increased significantly (P less than .001) and the ratio of apolipoprotein B to apolipoprotein A-I concentration decreased significantly (P less than .01) irrespective of gender. These data show that the levels of plasma apolipoprotein A-I, a strong predictor of coronary heart disease, are favorably affected by isradipine of either formulation. The mechanisms of this effect remain to be elucidated.