To examine temporal trends in ceftazidime resistance, susceptibility data reported to the National Nosocomial Infections Surveillance system during 1987-1991 were analyzed among nosocomial Enterobacter species, Klebsiella pneumoniae, and Pseudomonas aeruginosa. Linear increases in resistance were observed for Enterobacter species and K. pneumoniae. One hospital experienced a dramatic rise from 1.0% in 1987-1989 to 40% in 1990-1991 (P < .001) in ceftazidime resistance among K. pneumoniae isolates. No increase was observed during this period for P. aeruginosa. Logistic regression analysis confirmed these trends (or the lack thereof) for Enterobacter species and P. aeruginosa; for K. pneumoniae, ceftazidime resistance was found to be increasing among isolates from teaching hospitals and intensive care units. Ceftazidime resistance is an emerging problem that has the potential for dramatic increases. Selective pressures for the development of ceftazidime resistance need to be identified and addressed.