Exposure of mouse spermatozoa and oocytes duringin vitro fertilization (IVF) to lipopolysaccharide (LPS) and phorbol myristate acetate (PMA) activated macrophages (U937 cell line), but not unactivated macrophages cultureconditioned medium or control medium (RMPI+DMEM with 0.5% FBS) resulted in inhibition of IVF (87.2%), first cleavage (90.8%) and total blastocyst formation 97.5%). The direct coculture of the activated macrophages with 2-cell stage embryos resulted in arrested development (91.2%), an effect that was significantly diminished in the presence of monolayer of human endometrial stromal cells in the coculture (58.3%). In contrast, the majority of 2-cell embryos developed to blastocysts when exposed to unactivated macrophages, or macrophage-stromal cell cocultures (94.1%). The majority of 2-cell embryos cultured in control medium (DMEM/Ham's F12 with 2% FBS) developed to morulae (96.2%), then underwent growth arrest and degeneration. Furthermore, culturing blastocyst stage embryos in the above groups resulted in a significant enhancement of trophoblast outgrowth, particularly in coculture with activated macrophages as compared to any other group (P<0.005). There was a significant increase in the levels of TGF-β, GM-CSF, IL-1α, IL-1β, TNF-α, PGE(2), TXB(2) and LTB(4) released into the culture conditioned medium of activated macrophages compared to unactivated macrophages (P<0.001). These results suggest that the secretory products of activated macrophages, among them those determined in this study, in a stage-specific manner can directly effect sperm-egg interaction, early embryonic development and trophoblastic outgrowth. This data provides further support for the hypothesis that in endometriosis-associated infertility, continuous exposure of spermatozoa, oocytes and early embryos to activated macrophage-derived factors may play a vital role in their survival during transportation and fertilization as well as development during early embryonic stage.