A total of 105 patients (mean age 57, range 15 to 90) with serious infections were treated with intravenous ceftazidime, usually 2 g 8-hourly. Most patients had complicating factors such as major surgery, cancer, chronic obstructive lung disease, catheters or anatomical abnormalities. Eighty-seven infectious episodes in 77 patients could be assessed for efficacy. Bacteraemia was diagnosed in 26% of these episodes. Seventy-five per cent of infections were due to Gram-negative bacteria, Pseudomonas aeruginosa being the most frequent. The major sites of infections were the lower respiratory tract (30), the urinary tract (28), the soft tissues (9), the biliary tract (4), bones (4) and the ears (4). Overall, 67% of the patients were cured, 20% improved, 7% relapsed and 6% failed to respond. Among the 27 infections due to Ps aeruginosa, only two failures (in the same patient) and four relapses were recorded. However, in the two failures and in three other cases with persistent Ps. aeruginosa colonisation, the organism had become resistant to ceftazidime. Three failures were recorded in the seven Staphylococcus aureus infections included in this study. Superinfection occurred in four patients. Adverse events included rash (6), Clostridium difficile toxin-induced diarrhoea (3), transaminase elevation (3), weakly positive Coombs test (10). Ceftazidime appears to be safe and effective for the treatment of severe Gram-negative infections, including those caused by Ps. aeruginosa.