Cyclosporins has been shown to reduce renal perfusion and to decrease glomerular filtration rate. Experimental studies suggest that nifedipine might reverse this renal vasoconstrictive effect of cyclosporins. We studied renal hemodynamics of 5 cyclosporine-treated renal transplant recipients before and after 2 weeks of therapy with high-dose nifedipine (up to 120 mg/day). Pretreatment GFR and renal plasma flow (RPF) were decreased. Following administration of nifedipine, RPF increased by 18% (P<0.01), while GFR did not change. Filtration fraction decreased by 10.5% (P<0.01). Mean arterial pressure declined from 111±5 to 96±3 mmHg (P<0.01). Renal vascular resistance dropped by 25% (P<0.01). Calculated postglomerular plasma flow increased by 20.5% (P<0.01). Urinary albumin excretion rate was unaffected. Cyclosporine whole blood levels were unchanged. The increase in RPF and in postglomerular plasma flow suggests that high-dose nifedipine might lessen cyclosporine-induced glomerular and interstitial ischemia in renal allograft recipients.