The in vitro activity of imipenem against 3,496 Gram-negative strains isolated from 4,505 positive urocultures was determined. The effectiveness of imipenem was then compared with that of ampicillin, amoxycillin + clavulanic acid, ticarcillin, piperacillin, aztreonam, cefalotin , ceftazidime, cefoxitin, cefotaxime, norfloxacin, ciprofloxacin, amikacin, gentamicin, tobramycin, trimethoprim + sulfamethoxazole. Imipenem was active against all isolates, including Pseudomonas spp. known to account for a large portion of nosocomial infections and resistance to antibacterial drugs.