The effect of oral administration of activated charcoal on total body clearance of vancomycin administered intravenously (7.5 mg/kg) has been studied in normal rabbits and rabbits with induced renal failure. Gastric intubation of a single dose (10 g) of activated charcoal to normal rabbits did not produce a statistically significant effect on any pharmacokinetic parameter for vancomycin. The mean vancomycin clearances were (mean +/- s.d.) 80.82 +/- 6.8 and 75.24 +/- 9.61 ml/h/kg with and without activated charcoal administration, respectively. To examine whether renal failure would influence the effect of activated charcoal and enhance the systemic clearance of vancomycin, uranyl nitrate was used (0.75 mg/kg, i.v.) to induce acute renal failure in rabbits. The derived pharmacokinetic parameters of vancomycin were consistent with renal failure. No significant differences were observed in any of the calculated pharmacokinetic parameters between the control and charcoal treated rabbits. The lack of effect may be attributed to the large molecular weight of vancomycin.