We studied the tolerance and pharmacokinetic parameters of ciprofloxacin in (2 mg/kg, i.v.) in 45 chicks. Serum concentrations of ciprofloxacin at various times of drawing (15 min, 30 min, 1 hr, 3 hr, 6 hr, 8 hr and 12 hr) peaked in the first 15 min with a trough after 6 hr, and were completely absent after 8 hr. We found no neurotoxic effects or behavioral changes. Encouraged by a good tolerance for this quinolone, we conducted a preliminary study concerning the therapeutic efficacy of ciprofloxacin in 8 subjects of pediatric age (8-14 years) with urinary tract infections (UTI) that are resistant to classic antibiotics. The results and normality of hematologic parameters, checked before and after therapy, allow us to recommend the monitored use of ciprofloxacin in children with UTI resulting from bacteria resistant to other antibiotics.