Acute suppurative cholangitis is a serious complication in extrahepatic biliary tract obstruction. Bacteriological studies have shown that in these patients the bile cultures usually present several kinds of bacteria, especially Gram-negative aerobic bacteria such as E. coli and Klebsiella sp. The mortality rate in our patients with common bile duct stones and acute suppurative cholangitis is enhanced 5- to 10-fold. The aim of the present study was to analyse the bacterial properties of choledochal bile in a large number of patients with common bile duct stones, with or without acute suppurative cholangitis, and to determine the sensitivity of the isolated bacteria to several antibiotics used in clinical practice. The greatest sensitivity of the bacteria isolated from the common bile duct was seen for aminoglycosides (gentamicin and amikacin) and for cephalosporins, especially of the third generation (cefotaxime, ceftazidime, ceftriaxone and cefoperazone). Ampicillin showed a low sensitivity rate. The appropriate selection of the antibiotics used in acute suppurative cholangitis depends not only on the concentration of the antibiotic in the bile; a high plasma concentration is even more important to control the septic manifestations. A high excretion to the bile can affect the intestinal flora, leading to diarrhea (e. g. with cefoperazone). Ampicillin has been giving contradictory results in respect of bile and plasma concentrations. Gentamicin attains 30-40% of the plasma concentration in the bile, but persists for as long as 8 hours with excellent sensitivity and clinical efficacy. Amikacin reaches 44% of the plasma concentration with a very high sensitivity (96%).(ABSTRACT TRUNCATED AT 250 WORDS)