Fosfomycin trometamol (FT), an antibiotic active against the common urinary pathogens, may be demonstrated in adequate urine concentrations up to 36-48 h after a single oral dose of 1-2 g. This pharmacokinetic peculiarity seems to indicate that this antibiotic may be used in single doses in the therapy of lower urinary tract infections (UTIs) in infants and children. The efficacy and safety of FT in single oral doses was compared with those of netilmicin (NM), an aminoglycoside antibiotic with a demonstrated efficacy in bolus doses against UTIs, shown in a multicentric study. One hundred and thirty-five children with lower UTI, diagnosed on the basis of fever (less than 38 degrees C), erythrocyte sedimentation rate (less than 25 mm/l h) and C-reactive protein (less than 20 micrograms/ml), were included in the study: 71 received 2 g of FT, 64 5 mg/kg of NM. Cure, defined as persistence of sterile urine up to 30 days after therapy, was reached in 80.2% of children in the FT group and in 81.2% of children in the NM group. Persistence of infection was demonstrated in 7 and in 3 children, respectively. Recurrence of infection was noticed in 7 patients in the FT group and in 9 in the NM group. No differences between FT- and NM-treated children are demonstrable even if the patient population is analyzed according to the higher risk of UTI because of the presence of an anatomical and/or functional abnormality of the urinary tract or due to a previous tendency to recurrent UTIs. FT is as effective as NM in the treatment of lower UTIs in infants and children.