Four cases of women with biliary infection caused by Haemophilus influenzae type b are reported. The patients had underlying benign or malignant disease of the biliary tract. Haemophilus influenzae was isolated in pure culture from bile in all cases and also from blood cultures in three cases. The clinical condition of three patients was not severe, two of them recovering after surgery without antibiotic therapy. The fourth patient died of septic shock which occurred after liver biopsy. The frequency of biliary infections caused by Haemophilus influenzae has probably been underestimated because of the special nutritional requirements of this microorganism. The route by which Haemophilus influenzae reaches the biliary tract is not fully understood.