Glucan, a 1-3-polyglucosidic component of the cell wall of Saccharomyces cerevisiae, was evaluated for its ability to alter survival in rats with induced intraabdominal sepsis. In four groups, each of 15 rats, the bacteriological flora was changed into that of humans by giving the animals a meat chew. Intraabdominal sepsis was induced by resecting 1 cm of the intestine and reimplanting it in the abdominal cavity after reestablishing the intestinal continuity by one-layer end-to-end anastomosis. The rats were injected with either glucan or isovolumetric saline or benzylpenicillin or glucan plus benzylpenicillin. The results indicate no significant difference in mortality rate between the groups treated with either glucan or benzylpenicillin on the one hand and, on the other, the group given saline alone. However, the group treated with glucan plus benzylpenicillin differed significantly from the control group given just saline. The bacterial flora did not seem to be influenced by glucan administration. It is concluded that glucan has a clear effect on the survival rate of rats with induced peritonitis, probably by enhancing the activities of the reticuloendothelial system--an important part of the total host resistance.