Orthoclone (OKT-3), a monoclonal antibody, is an effective immunosuppressant in organ graft recipients. One of the reported side effects is serious pulmonary edema, heart failure, hyperdynamia, and elevation of blood pressure. It should be assessed whether patients treated with OKT-3 benefit from antihypertensive therapy with a calcium channel blocker before and during the allograft rejection therapy to prevent from cardiovascular side effects. To assess a preventive cardiovascular effect of therapy with nitrendipine before and during the OKT-3 rejection therapy, the patients studied (n = 28) were randomly allocated to two study groups. Group a without nitrendipine comprised 15 patients, and group b with 2 x 10 mg of nitrendipine daily comprised 13 patients. In study group a (without nitrendipine therapy), in 8 of 15 patients, there was a short-lasting increase in blood pressure during 3 h after the first injection of OKT-3 by 20.0 +/- 12.8 (systolic)/10.1 +/- 6.7 (diastolic) mm Hg. Whereas this initial rise of blood pressure on the first day was accompanied by an increase in heart rate by 24.1 +/- 10.8 beats/min, the longer-lasting increase in blood pressure at day 2 was not associated with significant changes in heart rate. In group b (patients receiving 2 x 10 mg of nitrendipine before OKT-3 therapy was started and during the whole treatment course), in 3 of 13 patients, a short increase in blood pressure (13.7 +/- 2.9/7.8 +/- 5.1 mm Hg) was recorded 5 h after the first dose of OKT-3.(ABSTRACT TRUNCATED AT 250 WORDS)