Cell to cell interaction play a major role in the induction of a immune response. NK cells represent a special lymphoid subset which displays its cytotoxic function without the engagement of MHC system. In order to investigate the role of different adhesion molecules in the mechanism of binding of the NK cell to the classic tumor target K562 cell, we have employed different unclustered mAbs of the Adhesion session (5th "CD" Workshop, Boston 1993) mostly of the CAM (cell adhesion molecule) subpanel. After their reactivity characterization both on lymphocytes and K562 cells, those that demonstrate reactivity against the tumor target were tested in the binding assay. The target was pretreated with the monoclonal in order to block a possible reacting molecule for the effector. Then, after the incubation of lymphocytes with PE-labelled anti CD16 mAb, their ability to bind to the target was tested in flow. While the majority of the mAbs did not induce any significant change in the binding capacity of the NK subset, few of them did, and precisely anti-CD58 (LFA-3) and anti-CD54 (ICAM-1) which showed different level of inhibition, particularly drastic with S002, S083 and S100. Other mAbs, such as the S011 (anti-CD59), due to the presence of the PI-linked glycoprotein recognized on both target and effector membranes, and to its capacity to stimulate NK activity, produced a total binding of the NK population. The coincubation of targets with anti-CD54 and anti-CD58 allowed to reduce at the lowest level this function. This data seem to support the hypothesis of specific surface molecules involved in the binding process of the NK cell, after recognition of the target.