The pharmacokinetics of fosfomycin, an original antimicrobial agent, were investigated in 11 voluntary hemodialyzed patients. Fosfomycin, 2 g, was administered intravenously, 15 minutes before hemodialysis began in group 1 (6 patients), and just after hemodialysis in group 2 (6 patients). Blood samples were collected during 8 hours (group 1) and during 44 hours (group 2). Antibiotic concentrations were determined microbiologically. In group 1, half-life was 4.2 +/- 0.27 hours, total clearance 65.1 +/- 7.1 ml/mn and clearance by hemodialyzer 103 +/- 10 ml/mn. In group 2 plasma levels were 60 mg/l at the 44th hour and half-life was 48.8 +/- 17.5 hours. These results suggest that fosfomycin is actively eliminated by the hemodialyzer in group 1, and largely retained between two dialysis sessions in group 2. As for therapy, intravenous administration of 2 g after dialysis and further administration after each succeeding session are proposed.