Uteroglobin, a steroid-dependent secretory protein first discovered in the rabbit uterus during early pregnancy, is a potent phospholipase A2 inhibitor. We found that uteroglobin also inhibited human and rabbit phagocyte chemotaxis in response to formyl peptide attractants in a dose-dependent manner. Half-maximal inhibition was at 1.2 microM. Uteroglobin did not compete with a formyl peptide for its receptor but inhibited internalization of radiolabeled formyl peptide. Uteroglobin appears to inhibit chemotaxis by a mechanism different from that of dansylcadaverine, a well studied inhibitor of endocytosis. Unlike dansylcadaverine, uteroglobin did not have any effect upon the synthesis of phosphatidylcholine or phosphatidylinositol. It is suggested that uteroglobin may protect trophoblastic cells from the defense system of the host not only by binding to antigenic determinants of embryonic cells but also by impairing migration of phagocytes, one of the primary components of the immune defense system. These results may explain why embryonic cells do not elicit an inflammatory response in the uterine endometrium during pregnancy.