The in vitro antibacterial activity of ciprofloxacin and 13 other antimicrobial drugs was evaluated with respect to 569 pathogens, mainly isolated from urine. Ciprofloxacin was found active in 96.1% of all of the Gram-positive and Gram-negative strains tested, amikacin in 90.6%, ceftazidime in 89.8%, ceftriaxone in 85.3%, piperacillin in 82.7%, tobramycin in 82.6%, gentamicin in 81.5%, aztreonam in 78.3%, nitrofurantoin in 72.6%, cotrimoxazole in 71.6%, cinoxacin in 71.0%, pipemidic acid in 70.6%, nalidixic acid in 66.7%, ampicillin in 50.1%. Ciprofloxacin was found to be the most active of the drugs studied against the bacterial strains which cause urinary, respiratory and other infections.