Effects of slowly performed daytime hemodialysis (slow HD) using a high-flux hemodialyzer on the pharmacokinetics of vancomycin were determined in 5 critically ill patients with renal failure. Following intravenous administration of 0.5 g of vancomycin, concentrations in the serum and dialysate were monitored. Pharmacokinetic parameters were calculated after fitting individual concentration-time curves to a two-compartment model. The volume of distribution at steady state was 0.58 +/- 0.12 liters/kg. Total body clearance was 37.46 +/- 3.20 ml/min with an elimination phase half-life of 8.72 +/- 0.99 h. Slow HD clearance was 20.19 +/- 2.30 ml/min. During a 10-hour session of slow HD, the serum vancomycin concentration decreased from 44.2 +/- 3.8 to 10.0 +/- 5.0 mg/l and 30.10 +/- 5.34% of the dose was eliminated. Dialyzer clearance of this drug and urea was 18.71 +/- 1.40 and 28.77 +/- 1.77 ml/min, respectively. Slow HD may effectively eliminate vancomycin by a diffusive mechanism and this elimination should be taken into consideration for designing the dosage schedule during the treatment.