Cell surface and cytoplasmic antigen expression by 35 CD3(-) decidual granular leucocyte (DGL) clones, derived from human endometrial tissue in the first trimester of pregnancy, has been compared with both that of fresh CD3(-) decidual leucocytes and that of CD3(-) peripheral blood natural killer (PBNK) cell clones (n = 12). The majority of DGL clones retained the antigenic phenotype of fresh cells, although CD103 (HML-1) was expressed on 50% of DGL clones but only 17% of fresh DGL. Both cytoplasmic CD3 zeta and CD3 epsilon chains were detected in > 90% of DGL clones in the absence of cell surface CD3. Cytoplasmic CD3 zeta was present in almost all fresh CD3(-) DGL, whereas CD3 epsilon was not. Most DGL clones did not express surface Fc gamma receptors I-III (CD64, -32 and -16, respectively) and complement receptors (CR) types 1 and 2 (CD35 and 21, respectively), but 43% expressed CR3 (CD11b/18); in contrast, all PBNK clones were CR3(+). The NK cell-associated molecules Kp43 (CD94) and the p58 molecule recognized by the HP3E4 monoclonal antibody were both present on a higher proportion of CD3(-) PBNK (91% and 50%, respectively) than DGL clones (31% and 14%, respectively), despite expression of CD94 by > 90% of fresh CD56(+) decidual leucocytes. Five of 35 CD3(-) DGL clones expressed cytoplasmic CD3 zeta in the absence of expression of CD2, CD16 or the p58 molecule recognized by HP3E4. These variations between CD3(-) DGL and PBNK cell clones in expression of functional molecules may be related to previously reported differences in major histocompatibility complex-non-restricted cytotoxic activities between these two cell types.