Cellular Ca2+ influx during the reperfusion period after an ischemic insult has been proposed to be a crucial pathogenetic factor in the development of experimental acute renal failure (ARF). The present study, therefore, examined the potential beneficial effect of intrarenal verapamil, a calcium entry blocking agent, on ARF in patients. Twelve patients were enrolled in the study. Six ARF patients (experimental group)--ARF caused by malaria (4 patients) and leptospirosis (2 patients)--had a catheter placed in their renal artery; verapamil was infused at 100 micrograms/min for 3 h and intravenous furosemide, 0.8 mg/kg/h x 24 h was also administered. Another six ARF patients (control group)--ARF caused by malaria (5 patients) and leptospirosis (1 patient)--were treated with intravenous furosemide alone. Baseline renal function was comparable in both groups; GFR (3.16 +/- 3.24 vs 0.7 +/- 1.5 mL/min, NS), serum creatinine (Scr), (9.1 +/- 2.1 vs 11.3 +/- 2.2 mg/dL, NS), and urine volume (V) (41.79 +/- 4.77 vs 34.54 +/- 13.52 mL/h, NS), were comparable in the experimental and control groups. Twenty-four hours posttreatment, the increment of GFR (9.66 +/- 4.25 vs 1.32 +/- 0.50 mL/min, P less than .02) and V (181.8 +/- 61.7 vs 79 +/- 18 mL/h, P less than .04), were significantly greater in the experimental group as compared to the control group. The course of ARF was also shorter in the experimental group (6.5 +/- 2.1 vs 13 +/- 1.1 days, P less than .05), who also required less dialysis. Thus, combination of a renal arterial infusion of verapamil and intravenous furosemide significantly improves the renal function in tropical ARF as compared to intravenous furosemide alone.