In order to assess the correlation between bacteria isolated from liver abscesses and factors predisposing to liver abscesses, a retrospective study of clinical and bacteriological data on 21 patients with 27 episodes of pyogenic abscesses was carried out at the University Medical Centre, Amsterdam. Out of 27 episodes, 15 (55%) were associated with biliary or pancreatic disease; in seven of these 15 episodes more than one microorganism was cultured. Enterobacteriaceae were isolated in 13 (85%) of 15 episodes. Anaerobic bacteria were recovered only when operations in the pancreatico-biliary area had been performed previously. Seven episodes (26%) were related to extrahepatic disease; anaerobic bacteria (Bacteroides and Fusobacterium spp.) were isolated in five of these seven episodes. Streptococcus milleri seemed especially prominent, since this bacterium was cultured in six of seven episodes. Enterobacteriaceae were not involved in these seven episodes. Other factors predisposing to liver abscesses (15%) were diabetes mellitus n = 2), paraproteinaemia (n = I), and metastatic carcinoid (n = I). Blood cultures were positive in 65% of 23 episodes, but 40% of the positive cultures contained a smaller number of bacterial species than could be cultured from the abscess itself. Bacteria isolated from liver abscesses are related to the underlying predisposing condition. For diagnosis of the underlying condition and antibiotic therapy, puncture and bacteriologic examination of the abscess is essential.