The effect of calcium salt of fosfomycin in the treatment of 43 neonates suffering from acute gastroenterocolitis produced by enteropathogenic E. coli is evaluated. The minimal inhibitory concentration of these E. coli was, generally, lower that 128 μg/ml. Dosages of 150–200 mg/kg body weight/day were administered orally every 8 h. This treatment lasted for 4 days only. Clinical evolution was favorable in 38 (88%) babies and bacteriological evolution in 30 (70%). In eight cases a different flora to the initial was selected during the treatment with fosfomycin. None of the cases treated showed any toxic alteration attributed to the antibiot