Exposure of the peritoneal cavity to meconium causes a marked inflammatory response. The effect of intraperitoneal meconium on intestinal morphology and plasma nitrite and nitrate (NO2(-) + NO3(-)) levels and how this inflammatory process is influenced by hyperbaric oxygen (HBO) treatment were investigated in this study. The purpose was to determine whether HBO treatment could be considered a useful adjunct in the resuscitative treatment of severely ill patients admitted with meconium peritonitis (MP). Rats were divided into three groups. Human meconium (MP group, n=10) and sterile saline (control group, n=10) were injected intraperitoneally for 3 days. The procedure for meconium injection was combined with HBO treatment for the HBO group (n=10). HBO was administered for 7 days. In all groups, peritoneal swap cultures, plasma NO2(-) + NO3(-) levels, intestinal diameters, and macroscopic and microscopic changes in the intestine were determined on the 8th day. Bacterial growth was not detected in the peritoneal swap cultures. There was a significant difference in NO2(-) + NO3(-) levels between the MP and HBO groups ( P<0.05), between the MP and control groups ( P<0.01), and between the HBO and control groups ( P<0.05). Thin fibrinous adhesions in both the MP and HBO groups, and thickened and dilated intestinal loops in the MP group were observed macroscopically. The intestinal diameter in the MP group was significantly greater than in the HBO and control groups. The only microscopic difference was seen in the serosal layer. Compared with the animals in the control and HBO groups, the intestine of the rats in the MP group showed prominent serosal thickening, edema, capillary proliferation and cellular infiltration. The ameliorated inflammatory changes and decreased dilatation of the intestine accompanied by a significant decrease in NO2(-) + NO3(-) levels suggest that as an adjunctive treatment, HBO may have a beneficial effect in the resuscitative treatment of meconium peritonitis.