Human milk appears likely to have anti-inflammatory properties but the data directly supporting this hypothesis are limited. We examined the effects of orally administered human milk, infant formula and animal chow in rats with chemically induced colitis (4% acetic acid enemas). Colonic myeloperoxidase activity was determined after extraction with hexadecyltrimethylammonium bromide buffer and used as a surrogate marker for neutrophil infiltration. Data are expressed as overall peroxidase activity/mg tissue (Mean±SE). A control group of rats with no colitis, fed with rat chow demonstrated low levels of colonic peroxidase activity (1.03±0.13 units/mg tissue). Rats with colitis fed infant formula (3.68±0.49 units/mg of tissue) or animal chow (2.23±0.25 units/mg of tissue) had significantly higher overall peroxidase activity in their colons compared with rats fed with human milk (1.44±0.2 units/mg tissue, both p<0.01). The largest differences in peroxidase activity were seen in the more proximal segments. These data show that human milk feeding decreases the neutrophil inflammatory response in animals. They suggest that human milk may have a biological anti-inflammatory activity in the intestinal tract of newborns and infants.(Supported by an Eastern Virginia Medical School Postdoctoral Fellow Research Award and by NIH HD-13021).