Cholangitis results from bacterial infection of the bile combined with biliary obstruction. There are surprisingly few large, recent series on biliary tract pathogens and antibiotic therapy in this clinical setting. AIM & METHODS: A prospective study of pathogens and antibiotic sensitivities in patients with cholangitis. The diagnosis was made clinically and blood taken for cultures and sensitivities to several antibiotics. RESULTS: There were 49 suspected cases of cholangitis from 45 patients. 23 positive blood cultures were obtained, giving a positive blood culture in 47% of cases. The underlying cause of their biliary obstruction was varied; bile duct stones, bile duct strictures, both benign and malignant, the presence of a blocked biliary stent make up the vast majority of diagnoses. 2 of the cultures were polymicrobial; E. coli and Enterococcus faecalis on both occasions. 14 isolates were E. coli, including the 2 above, 2 isolates were Klebsiella spp, 1 isolate was Enterobacter cloacae, 1 isolate was an unidentified coliform spp, 1 isolate was Pseudomonas aeruginosa, 5 isolates were Enterococcus spp, 1 isolate was Veillonella spp. Sensitivities to the all coliforms: Ciprofloxacin 17 out of 17 (one not tested), Pseudomonas was also sensitive to this, Cefuroxime 17 out of 17 (one not tested), Cefotaxime 18 out of 18, Augmentin 15 out of 17 (one not tested), Gentamicin 18 out of 18, including Pseudomonas. Enterococci were resistant to all cephalosporins and aminoglycosides and had intermediate resistance to ciprofloxacin. Pseudomonas aeruginosa was uniformly resistant to all second and third generation cephalosporins. Veillonella, the only anaerobe, was sensitive to penicillin and metronidazole. CONCLUSION: The initial antibacterial therapy in cholangitis should be a cephalosporin (cefuroxime or cefotaxime) or ciprofloxacin. For second line we suggest the addition of metronidazole or augmentin (theoretical benefits of augmentin to enterococci).