We examined the occurrence of renal complications and hypertension in 540 primary liver recipients entered into the European liver trial comparing primary FK 506 to a cyclosporin A based immunosuppression regimen (CBIR). No difference in serious renal impairment or mean creatinine levels was observed with similar rates of "kidney failure" (FK 506 9.4% vs. CBIR 7.3%) and dialysis requirements (FK 506 12% vs. CBIR 11%). "Abnormal kidney function", a less serious parameter of renal impairment, was reported in 89 recipients (33%) in the FK 506 group versus 58 (21%) in the CBIR group (P < 0.01). Development of this complication was associated with elevated intravenous FK 506 dosing schedules, with the mean cumulative dose 43% higher than treated patients with unaffected kidney function. In a later cohort of patients where intravenous dosing was lower, no significant difference in renal complications was detectable. The 6-month prevalence rate of systemic arterial hypertension was noted to be lower in the FK 506-treated patients compared to the CBIR group [33 (17.2%) vs. 47 (25.7%)].