Granulated lymphoid cells (CD2+, CD7+, CD38+, NKH1+, CD3-, CD5-, CD4-, CD8-, CD25-) are prominent in human endometrial stroma in the late secretory phase of the menstrual cycle and in early pregnancy, and may play an important role in implantation and placentation. Cell suspensions enriched for granulated lymphoid cells were prepared from first trimester human decidua using a panning technique; cells were labelled with the monoclonal antibody NKH1 and separated by adherence to immunoglobulin-coated plates. The enriched cells were characterized with a panel of monoclonal antibodies using an indirect immuno-alkaline phosphatase method, and subjected to various functional assays. Most cells in the enriched preparations showed the characteristic morphology of granulated lymphocytes in smears stained with toluidine blue or May Grunwald Giemsa. CD45+ cells were obtained up to 98+/-1% purity (n= 10) and CD2+ cells were enriched up to 84+/-4%. The enriched populations were efficient effectors in a K562 chromium-release assay but showed minimal proliferative response to phytohaemagglutinin, concanavalin A, ionomycin and phorbol 12, 13 dibutyrate (PdBU), interleukin 1 or interleukin 2. The precise lineage and in vivo function of decidual granulated lymphocytes remains to be established.