The pharmacokinetics of fosfomycin in humans was studied in six young healthy volunteers after intravenous administration of 500 mg fosfomycin and after the same dose in oral administration in three different formulations. It was proven that fosfomycin follows a bicompartmental pattern, for which the disposition constants, the biological half-lives for the fast and slow phases, and the distribution constants were calculated. The renal excretion constant was evaluated making determinations of fosfomycin in the urine, and this constant together with the elimination constant allowed us to determine the extrarenal elimination. The concentration and quantity of the drug in the central and peripheral compartments were calculated and tabulated for different periods of time. An analogous behavior was obtained with the three formulations that were orally administered, with an average bioavailability of 37% in relation to the intravenous bioavailability, as evaluated by means of the accumulative renal excretion.