Data on the adverse effects experienced by 2,539 patients who received ceftazidime were compared with adverse effects reported with cefoperazone, cefotaxime, ceftizoxime, and moxalactam. There were 216 such reactions among the ceftazidime-treated patients; 158 patients (6.2 percent) had reactions that were possibly or probably drug-related. The clinical and laboratory safety profile of ceftazidime in regard to renal, hepatic, hematopoietic, and hemostatic parameters compared favorably with that of other third-generation cephalosporins. An increased serum creatinine level was observed in 0.8 percent of ceftazidime-treated patients, an increased blood urea nitrogen level in 1.6 percent, hepatic abnormalities in approximately 6 percent, diarrhea in 1.3 percent, pseudomembranous colitis in 0.12 percent, increased prothrombin time in 0.5 percent, and clinical bleeding in none. The incidence of colonization (3.8 percent) and superinfections (3 percent) associated with ceftazidime therapy was comparable to rates with other agents in this class.