The aim of the present study was to determine the effect of a calcium channel blocker on renal function, urinary endothelin excretion and endothelin receptor number in rats. Administration of cyclosporine resulted in a significant impairment of renal function when measured by either [14C]inulin or 24 h creatinine clearances. This nephrotoxicity was associated with statistically significant (P less than 0.05) increases in urinary endothelin excretion and renal endothelin receptor number. Treatment with nifedipine attenuated cyclosporine A-induced renal dysfunction and reduced urinary endothelin excretion. The data provide further evidence of a role for endothelin in cyclosporine A-induced nephrotoxicity.