A prospective, randomized study was undertaken to compare the efficacy and safety of tobramycin and ceftazidime in the treatment of serious infections in 77 urological patients. Of the 39 tobramycin-treated and 38 ceftazidime-treated patients, 74% and 82%, respectively, were cured clinically. Microbiological cure rates were 72% and 79%, respectively. Three patients treated with tobramycin and two treated with ceftazidime developed a significant superinfection. Both drugs were tolerated well. Because of potential ototoxicity and nephrotoxicity the use of aminoglycosides is less advantageous than ceftazidime for seriously infected urological patients.