The pharmacokinetics of intravenously administered levofloxacin and ciprofloxacin were studied in intensive care unit patients during continuous venovenous hemofiltration (CVVH; four patients received levofloxacin, and five received ciprofloxacin) or hemodiafiltration (CVVHDF; six patients received levofloxacin, and five received ciprofloxacin). Levofloxacin clearance was substantially increased during both CVVH and CVVHDF, while ciprofloxacin clearance was affected less. The results of this study suggest that doses of levofloxacin of 250 mg/day and ciprofloxacin of 400 mg/day are sufficient to maintain effective drug concentrations in the plasma of patients undergoing CVVH or CVVHDF.