The effect of regional abdominal heating on the small and large bowel was evaluated in three female research pigs. The BSD Annular Phased Array was used for heating. Blind-end catheters and a free peritoneal probe were surgically attached to small bowel, large bowel, liver, and kidney. Each pig underwent 4-8 heating sessions and was subsequently autopsied. There was no histologic evidence of acute bowel, liver, or kidney damage. There were significant differences in temperatures at the various sites. The average small bowel temperature was significantly higher than predicated by the free peritoneal probe or than seen in the liver or kidney. The large bowel temperatures averaged higher than the free peritoneal probe temperatures, but the difference was not significant. Liver and kidney temperatures approximate whole body temperature due to extensive vascular network. Although the elevated small bowel temperatures may be due in part to different position in relation to isotherms, the frequent occurrence of a large temperature difference suggests focal heating of fluid pockets in the small bowel.