The results obtained from the test of the in vitro activity of Fosfomycin by a concentration of 104 bacteria/ml and by Nutrient Broth with 5% defibrinated blood, have shown that the drug has a capacity of action on both Gram-negative and Gram-positive germs, also on beta-lactamase producing bacteria. Fosfomycin is a bactericidal antibiotic. infact the M.I.C. values are simjlar to M.B.C. values.