A study was made of the elimination of fosfomycin by the membrane of the artificial kidney in 10 patients with hemodialysis and a creatinine clearance of less than 5 ml/min. To do so we determined the half-life, the dialysance, the percentage of total loss and the percentage of loss by the artificial kidney. We reached the conclusion that fosfomycin is heavily dialyzed (D = 64 ml/min), it is entirely eliminated by the kidneys and its half-life is therefore affected very little (an increase of only about 30 min is produced). All of this leads to a practical schema by which the entire initial dose should be replenished at the end of each dialysis.