We have investigated, using flow cytometry, the expression of 19 adhesion molecules on fresh and IL-2-activated NK cells. The study included beta 1, beta 2 and beta 3 integrins, CD2, CD54 and CD58 (belonging to the immunoglobulin superfamily), and CD44 and L-selectin (homing receptors). alpha 1 and alpha 2 of the beta 1 integrins were non-existent and alpha 3 was weak on freshly isolated NK cells, but their expression increased after 4 weeks in culture with IL-2. On the other hand, some down-regulation of alpha 4 and alpha 5 and disappearance of alpha 6 was detected. CD 11a/CD18 was upregulated by IL-2, whereas CD11b-c/CD18 were down-regulated. As a novel finding we detected beta 3 on IL-2-activated T and NK cells. CD2, CD44, CD54 and CD58 were increased by IL-2 but L-selectin was strongly down-regulated on the long-term-activated NK cells. Although IL-2-activated lymphocytes are potent tumor-lysing killer cells in vitro and therefore a potential modality in cancer treatment, the IL-2 induced changes in lymphocyte adhesion molecule expression may also lead to undesired effects, such as altered untargeted distribution and compromised migratory capacity.