A clinical test was carried out on 83 children suffering from infectious diarrhoeal processes who were treated with fosfomycin with the oral and paranteral route. Coproculture was carried out in all the children before the beginning of treatment and in 51 of them it was repeated at the end of treatment. Antibiograms were made on the isolated germs and their MIC to fosfomycin studied. Tolerance and secondary effects of the medicament were also studied. The study was considered insufficient in 13 patients so that the evaluation was based on 70, making 4 failures and 66 clinical cures. Administration of fosfomycin causes the eradication of serotypeable E. coli and is followed by an increase in the number of Proteus sp. and Klebsiella/Enterobacter. The sensitivity of the faecal flora to fosfomycin has been very high, except for the strains of Proteus sp. and Klebsiella/Enterobacter. The accumulative percentage of the MIC to fosfomycin of all the strains isolated shows that more than 75% of them are inhibited at concentrations under 32 μg/ml. Tolerance was good and no secondary effects were observed except for the sporadic rise in the SGPT of the children