There is evidence that calcium antagonists may have a beneficial effect on cyclosporin A (CyA)-induced hypertension after organ transplantation. In a double-blind controlled trial, 50 consecutive non-diabetic first kidney-transplant recipients were randomized to receive either isradipine, a dihydropyridine calcium antagonist, or placebo. There were no significant differences in age, weight, gender, warm and cold ischaemic periods, and original renal disease between treatment groups. Treatment was started intravenously 2 h before the transplantation procedure and was subsequently continued orally for 3 months. The immunosuppressive treatment included oral CyA from day 5 after a short course of anti-T-lymphocyte immunoglobulins. Hypertension was treated with oral labetolol in combination with guanfacine if necessary. Antihypertensive medication was prescribed significantly more often (16 vs 7 patients; p < 0.05) in the placebo group. Standing systolic blood pressure was significantly lower in the isradipine group. The standing diastolic and both systolic and diastolic sitting blood pressures were similar in both groups. After 3 months, patients' mean serum creatinine was significantly lower with isradipine than with placebo (142.0 +/- 11.9 vs 164.0 +/- 10.8 mumol/l; p < 0.05). With isradipine, a significantly higher dose of CyA was needed to achieve adequate plasma levels (8.0 +/- 0.5 vs 6.2 +/- 0.5 mg/kg/day; p < 0.01). It can be concluded that isradipine is an effective antihypertensive agent after kidney transplantation and may have an influence on CyA metabolism. Furthermore, isradipine appears to ameliorate CyA-induced nephropathy.