Separate groups of mice were fed either standard rodent chow or one of three liquid diets (Impact, Isosource HN, Fibersource HN) for 14 days to determine the effects of these liquid diets on the cecal bacterial flora and on the incidence of bacterial translocation to the mesenteric lymph nodes. Liquid Isosource and liquid Fibersource had no noticeable effect on either the cecal bacterial flora or the incidence of bacterial translocation. Liquid Impact was associated with cecal bacterial overgrowth but had no effect on the incidence of bacterial translocation. Each of the liquid diets was then lyophilized and similarly fed to mice; none of the lyophilized diets had a noticeable effect on the cecal bacterial flora or the incidence of bacterial translocation. To test these liquid and lyophilized diets in stressed mice, separate groups of mice were again fed the various diets for 14 days but given parenteral Escherichia coli lipopolysaccharide (LPS) 24 h before being killed. None of the liquid or lyophilized diets had a noticeable effect on the cecal bacterial overgrowth noticed in LPS-treated chow-fed mice. Compared with chow-fed mice, the typically elevated LPS-induced bacterial translocation was even more elevated in mice fed liquid diet but was somewhat decreased in mice fed lyophilized diet. Thus, the modulatory effects of these liquid diets on the cecal flora and the incidence of bacterial translocation appeared to depend on the composition of the diet and on prior treatment with parenteral LPS.