Attempts were made to find and characterize an antibacterial activity (ABA) factor in porcine pancreatic juice (PJ). Its isolation requires several steps. Since ABA factor was found to be heat resistant, the first step was heating for 30 min at 65 degrees C. Afterwards column chromatography, ethanol precipitation and polyacrylamide gel electrophoresis were involved. Finally, we obtained a pancreatic juice fraction with antibacterial activity against Escherichia coli strain AB1157. In the presence of this fraction the number of living bacterial cells in overnight culture decreased about 10,000 fold and a spot-test gave clearly positive results. The results of analysis suggest that the antibacterial factor is a polypeptide active in a pH range 8.0-8.5, that migrates in polyacrylamide gel electrophoresis as a band under 14,000 Da. Mass spectroscopy analysis of active fraction showed high concentration of porcine pancreatic spasmolytic polypeptide (PSP). In conclusion, a polypeptide controlling bacterial homeostasis has been found in the porcine pancreatic juice.