Objective: To assess prospectively the effectiveness of a single prophylactic dose of cefuroxim before therapeutic endoscopy, in view of the general practice not to give antibiotics routinely. Patients and methods: In a prospective study endoscopic retrograde cholangiopancreatography (ERCP) or percutaneous transhepatic cholangiography with drainage (PTCD) together with simultaneous stone extraction, dilatation or stent implantation were performed in 99 patients (51 men, 48 women; mean age 60.6 +/- 19.2 years). Group A (n = 49) received 1500 mg cefuroxim i.e. 30 min before the procedure, while none was given to group A patients (n = 50). Several blood cultures were taken up to 60 min after the endoscopy. The number of septicaemias (bacteraemia with fever, rigor, circulatory reactions, leukocytosis or leukopenia) were noted. Bile cultures were obtained in 56 patients with indwelling biliary drainage. Results: Incidence of bacteraemia was 6.1 % (3 of 49) in group A, 16% (8 of 50) in group B, but this difference is not statistically significant. The septicaemia rate was 6.1% in group A and 10% in group B (not significant). There were eleven positive blood cultures with 12 different microorganisms, Escherichia coli in four (A: n = 3). In vitro cefuroxim sensitivity was 53.3%. 25 different bacterial species were isolated from 73,2% of bile cultures, of which 53.4% were sensitive to cefuroxim and 8.2% moderately so. Conclusion: Although the obtained differences between the two groups were not statistically different, the reduction in bacteraemia/septicaemia Fate may be of clinical use. Further studies are needed with higher dosages or antibiotic combinations to improve these results.