Fifty-one children suffering from symptomatic and asymptomatic recurrent urinary tract infections were treated at random in a comparative study. A single dose of 2 g fosfomycin trometamol was administered to 24 children (2 males and 22 females, mean age 6.7 +/- 3.3 yr) and two 200 mg doses of pipemidic acid (400 mg in children weighing more than 25 kg) were administered daily to 27 children (3 males and 24 females, mean age 6.6 +/- 3 yr) for 7 days. Bacteriological results showed that at the end of followup (1 month) urine was sterile in 17 out of 24 children treated with fosfomycin trometamol (70.8%) and in 19 out of the 27 children treated with pipemidic acid (70.3%). One persistant infection and six reinfections were observed in the follow-up period in the fosfomycin group and 8 reinfections in the pipemidic acid group, usually in patients with urinary complications. No side effects were reported. The microbiological study of feces showed that neither of the drugs caused the emergence of resistant bacteria.