We have recently reported a simple technique for the purification of large granular lymphocyte/NK cells with broad anti-tumor cytotoxicity (lymphokine-activated killer (LAK) activity) by the induction of their adherence to plastic surfaces by recombinant IL-2. Using this technique with nylon wool passed human peripheral blood or splenic lymphocytes we generated populations of adherent LAK (A-LAK) cells which were 80 to 95% large granular lymphocyte and up to 97% Leu-19+ cells. Using two-color fluorescence and cell sorting we now demonstrate that these same cells express a high density of surface structures which are immunochemically cross-reactive with affinity purified anti-laminin antibody. Laminin-like structures were expressed on 80 to 90% of Leu-19+/CD3- LAK cells but were not expressed on resting CD3+/CD4+/Leu19- T cells or CD3+/CD8+/Leu19- T cells. Laminin-like molecules were also expressed on resting Leu19+/CD3- large granular lymphocyte/NK cells (purified to more than 98% by cell sorting) and increased in intensity as these cells developed LAK activity in response to rIL-2. The functional involvement of laminin-like molecules in NK and LAK cytotoxicity was demonstrated by the ability of affinity purified anti-laminin F(ab')2 antibody to inhibit cytolytic activity in a dose-dependent manner (50% inhibition with 10 to 20 micrograms F(ab')2). Analysis of the mechanism of inhibition using single cell cytotoxicity assays indicated that the laminin-like structure was involved in activation of cytotoxicity and not in primary target cell adhesion. We believe that this structure may function as a novel recognition/activation structure used by cells mediating non-MHC restricted cytotoxicity.