Results are presented for a series of 29 patients, 14 males and 15 females, with serious respiratory infections, in which fosfomycin proved effective. In all cases the study was completed by bacteriological, clinical, radiological and analytical controls. The average dose was 6 g/day (3 g orally and 3 g intramuscularly) for 1 or 2 weeks. The four isolated were P. aeruginosa, E. coli, Klebsiella-Enterobacter and D. pneumoniae. Overall sensitivity percentages were best for fosfomycin, gentamicin and colistin. Of the 29 germs isolated, only one strain of P. aeruginosa became resistant: this represents 3% resistance development. No side effects of intolerance or signs of hepatorenal insufficiency were observed during the treatment. Of the 29 patients treated, 22 were clinically cured, denoting 76% success.