To examine the dietary effects of three lipids from different sources on intes-tinal conditions, diets containing 10% corn oil (CO), 1% corn oil +9% beef tallow (BT) or 1 % corn oil + 9 % menhaden fish oil (MO) were administered to male mice for 4 wk. Levels of total cholesterol (TC), non-esterifide fatty acids (NEPA) and glucose in plasma were lower in mice fed on MO than in mice fed on CO or BT. The plasma phospholipid (PL) level was lower for mice fed MO than in mice fed BT. Levels of the thiobarbituric acid-reactive substances (TBARS), soluble saccharides and soluble proteins in the cecum were significantly higher in mice fed on MO than in mice fed on CO or BT. The number of fecal bacteroidaceae was lower in mice fed on MO than in mice fed on BT. On the other hand, the number of fecal bifidobac-teria was greater in mice fed on MO than in mice fed on CO. These results suggest the possi-bility that menhaden oil affects lower intestinal microfiora through the increase of not only oxide products but also saccharides and proteins in the intestine.