The pathogenesis of sepsis in acute pancreatitis is unknown. Since the intestinal tract has recently been identified as a possible source for sepsis in other conditions, we explored whether the gut may serve as a reservoir for bacteria causing systemic and pancreatic infection in acute pancreatitis. Bacterial translocation, alterations of intestinal microflora, and intestinal motility, as reflected by gut propulsion, were studied in a rat pancreatitis model. Acute pancreatitis was induced by biliopancreatic obstruction (AP); sham manipulated animals served as controls (sham). Bacteriologic cultures were obtained from various segments of the intestinal tract and from blood, liver, spleen, pancreas, and mesenteric lymph nodes 48 and 96 hr after induction of AP or sham. Bacteria were recovered from mesenteric lymph nodes of all 12 animals with AP, but only from 3 14 sham animals ( P < 0.05). Spread to distant organ sites occurred in 4 of 12 animals with AP compared to none of the sham animals ( P < 0.05). A disruption of the intestinal microflora was found in the cecum, where the gram-negative bacterial count (log/g) was significantly higher during AP when compared with sham controls: 10.62 ± 1.04 vs 8.05 ± 1.45 at 48 hr and 7.92 ± 0.62 vs 6.79 ± 0.87 at 96 hr, respectively. In addition, the gram-negative bacterial population was also significantly increased in the duodenum of animals with AP after 96 hr as compared to sham: 5.10 ± 0.97 vs 3.94 ± 0.81. Small bowel propulsion was studied 24 hr after induction of AP or sham by injecting fluorescent-labeled dextrans into the duodenum and measuring the distance that the dextrans migrated distally after various time periods. The mean reduction of gut propulsion was 55% at 25 min, 34% at 60 min, 36% at 120 min, and 27% at 240 min. These data implicate the gut as an important source for infection during acute pancreatitis. A possible mechanism for the development of sepsis appears to be decreased gut motility followed by a disruption of the indigenous microflora with subsequent promotion of bacterial translocation to mesenteric lymph nodes and distant sites.