Biliary stones are the most common etiology of acute pancretitis (AP). Pathomechanism of this etiology is based on common channel theory of Opie.Material and methods. 113 patients with ABP were included in the study - 91 with mild and 22 with severe form of ABP. 17 patients with cholelithiasis and choledocholithiasis without ABP served as controls. All the patients were submitted to the same model of treatment. Endoscopic retrograde cholangiopancreatography (ERCP) with endoscopic sfincterotomy (ES) were performed in the day of admission and laparoscopic cholecystectomy within the next 24 hours. Bile specimens were taken from main bile duct (MBD) during ERCP and from gall-bladder (GB) during laparoscopic cholecystectomy. Bacteriological cultures, bile acids (BA) concentration and total and secretory form of IgA concentration were assessed in particular groups of patients.Results. No significant statistical differences of bile infection in MBD and GB were found between the analyzed groups of patients. Furthermore, the bile among the patients with severe ABP was more frequently infected, particularly when obtained from gall-bladder. Most common pathogens found in cultures were Gram negative bacteria. Interestingly, Gram positive cultures and fungi were also significant. The number of species of pathogens was of no significance for infection concerning both: source of bile and groups of patients. Mean concentrations of total BA were different between study groups of patients in MBD and in GB. It is worth mentioning, that the fraction of hydrophobic, secondary BA which are potentially more toxic, was increased in total concentration of BA in MBD particularly in patients with severe form of AP. Among patients with mild AP and controls these values were lower and similar.Conclusions. It seems that BA play as an aggressive factor during AP while in physiologic condition have a protective, antibacterial meaning.