Abstract. Lymphocyte function-associated antigen-1 (LFA-1) is a leukocyte and lymphoma cell surface protein that promotes intercellular adhesion. We have previously shown that the invasion of hepatocyte cultures by lymphoma cells is inhibited by anti-LFA-1 antibodies (Roos, E., and F. E Roossien. 1987. J. Cell Biol. 105:553-559). In addition, we now report that LFA-1 is also involved in invasion of lymphoma cells into fibroblast monolayers.To investigate the role of LFA-1 in metastasis of these lymphoma cells, we have generated mutants that are deficient in LFA-1 cell surface expression because of impaired synthesis of either the ~ or ~ subunit precursor of LFA-1. We identified at least three distinct mutant clones. The invasive potential of the mutant cells in vitro, in both hepatocyte and fibroblast cultures, was considerably lower than that of parental cells.The metastatic potential of the mutants was much reduced, indicating that LFA-I expression is required for efficient metastasis formation by certain lymphoma cells.