Using an enzyme-bridge immunoperoxidase (PAP) technique, it was revealed that pregnancy- and/or placenta-specific proteins, SP1, PP10 and PP12 were localized in human and cynomolgus monkey (Macaca fascicularis) polymorphonuclear neutrophils, and PP10, in mononuclear phagocytes. There was no difference in staining results, irrespective of whether the specimens were from human or monkey males, or pregnant or nonpregnant females. The results suggest that SP1, PP10 and PP12 may be synthesized by polymorphonuclear neutrophils and/or mononuclear phagocytes and could represent markers not only for trophoblasts and some kinds of malignant neoplasms but also for normal neutrophils and/or monocytes.