Fosfomycin has been used on 40 patients with serious urinary infections of different clinical nature, and produced by repetitive infection (prostatisms, carcinomas, lithiasis, hydronephrosis, etc). The following were isolated in the uro-cultures: E. coli (60%), Klebsiella (15%), P. aeruginosa (15.0%), Proteus sp. (15.0%) Staphylococcus (5%), S. faecalis (2.5%) and Paracolobactrum coliforme (2.5%). All the germs isolated before treatment were sensitive to fosfomycin. The results, as regards response to the bacteriuria, were 71.4% eradication of the infection, 17.2% reinfections and 11.4% failures. The results are considered very satisfactory in view of the etiopathogenic nature of the processes under treatment.