Cyclosporine decreases renal perfusion and impairs the renal hemodynamic response to a protein load. High-dose nifedipine has been shown to elevate renal plasma flow (RPF). We measured the renal functional reserve of 6 cyclosporine-treated renal-transplant recipients following intravenous administration of an amino acid solution, before and 2 weeks after therapy with high-dose nifedipine (up to 120mg/day). Pretreatment renal functional reserve was nil. Following administration of nifedipine, RPF increased by 22% (p < 0.01), filtration fraction decreased by 14% (p < 0.005) and renal vascular resistance declined by 39% (p < 0.005). Renal functional reserve remained unchanged. High-dose nifedipine incrases renal perfusion but does not restore renal functional reserve in cyclosporine-treated renal-transplant recipients.