Norfloxacin (MK-0366) is a new antibacterial agent, closely related to nalidixic acid, with broad spectrum activity against Gram-positive and Gram-negative organisms, including Pseudomonas aeruginosa. A clinical study was conducted on forty hospitalized patients with bacteriologically proven urinary tract infections; 20 patients were given norfloxacin and 20 co-trimoxazole. Clinical results were excellent in both groups; norfloxacin was effective in infections due to Ps. aeruginosa and other multi-resistant pathogens. No side effects were reported.