This study clarified changes in the serum amikacin (AMK) levels in the blood of 5 patients (4 men and 1 woman; average age 59.2 +/- 5.9 years) with serious acute renal failure treated by continuous arteriovenous hemofiltration (CAVH). The following principal results were obtained. (A) The average remaining rate of AMK in the blood after 6 h was 60.8 +/- 5.3% and 50.4 +/- 5.3% after 12 h. The average half-life period (t1/2 beta) of AMK in the blood during CAVH was 18.3 +/- 3.4 h. (B) The remaining rate of AMK in the blood after 12 h correlated significantly with the blood urea nitrogen (BUN) level (r = 0.71, p less than 0.05) and with the volume of urine excreted per day (r = -0.71, p less than 0.05). (C) The average lowest AMK concentration after 24 h for a continuous 17-day period was 3.3 micrograms/ml. These results suggest that the administration of 100 mg of AMK once a day is useful and safe for patients with serious acute renal failure treated by CAVH and that it will not accumulate in the body.