We compared the effects of 4 weeks of calcium channel blockade (amlodipine) or converting enzyme inhibition (lisinopril) on blood pressure and renal hemodynamics in a double-blind crossover trial in a group of 20 hypertensive cyclosporine-treated renal transplant patients. Amlodipine (10 mg) was more effective than the same dose of lisinopril in controlling hypertension (mean 24-hour arterial pressure, 111 plus/minus 9 and 115 plus/minus 9 mm Hg, respectively; P < .05). Blood pressure during both treatments was lower than during placebo (124 plus/minus 12 mm Hg, P < .05). Compared with placebo, amlodipine treatment was associated with a significant increase in glomerular filtration rate (10 plus/minus 20%, P < .05) and effective renal plasma flow (27 plus/minus 20%, P < .01) and a decrease in renal vascular resistance (23 plus/minus 18%, P < .01). Renal hemodynamics did not change during lisinopril. Neither drug had an effect on proteinuria. The data indicate that amlodipine is more effective than lisinopril in controlling hypertension in cyclosporine-treated patients and that treatment with amlodipine but not with lisinopril is accompanied by an increase in glomerular filtration rate and effective renal plasma flow and a decrease in renal vascular resistance. The data suggest that the renin-angiotensin system does not play a main role in determining cyclosporine-associated changes in renal hemodynamics and has a limited role in determining cyclosporine-associated hypertension. (Hypertension. 1995;25:77-81.)