The recognition of effector cell populations that are able to actively from conjugates with target cells is of major importance in studies of lymphocyte cytotoxicity. A number of methodologies have been described to identify the conjugates and count them, but there have been few studies of the binding capability of the different subsets of effector cells involved in the conjugation phenomenon. Here we describe a methodology that permits the study of two surface markers on lymphocytes conjugated to K562 target cells. In particular, the expression of low density CD8 (CD8dim) has been studied on both CD3+ and CD16+ lymphocytes bound to K562 target cells. Previously described methodologies, either optical microscopy or flow cytometry, were not able to identify the effector population by mAb double staining, especially in the case of antigens expressed at low density. The flow cytometric methodology described here permits the measurement of the binding activity of small lymphocyte subsets such as the CD3+ 8dim+ population. However, the method could be used to study the binding activity of any effector population defined by mAb double staining.