The authors compared short-term and ultrashort-term antibiotic prophylaxis with ceftazidime for the prevention of infections in selective biliary surgery. The multicenter (180 centers) study involved 1800 patients; at present data are available for 44 centers (392 patients, 129 males, 263 females, age range 18-87 years). Treatment schedule consisted of a single i.v. administration of 2 g ceftazidime concurrent with anesthesia induction (group 1) whereas short-term prophylaxis comprised administration of 1 g ceftazidime with preanesthesia, 30 min before the beginning of surgery and 6 and 12 hrs. after the first dose (group 2). The two groups (193 and 199 patients respectively) were similar for age, sex, concomitant pathology, presurgical diagnosis, risk factors (both as to incidence and type), biliary drainage. The difference in success rate between the two groups was 2.3% (92.2% in group 1; 94.5% in group 2) with a 90% confidence interval of 2.4 and 6.9%; this difference was not significant (p = 0.491). These preliminary findings indicate the administration of a single dose of ceftazidime as a valid alternative to short-term prophylaxis in view of its practical and economic advantages.