The attachment to and penetration of basement membranes by tumor cells is required to complete the metastatic cascade which culminates in the establishment of secondary tumor foci. Therefore, basement membranes are critical barriers to the passage of disseminating tumor cells. We have developed a simple, in vitro model using matrigel-coated transwell chambers (Costar) for use in a tumor cell invasion assay. Two variants of the K1735 UV-induced murine melanoma cell line were assayed for their invasive capabilities and compared with their ability to colonize the lung in an experimental metastasis assay. The K1735-M2 cells, which are highly metastatic in vivo, invaded through basement membrane matrigel at a significantly higher rate than the low metastatic cells, K1735-16, in a 72-hour assay. As a negative control, normal murine fibroblasts were incapable of penetrating the barrier. Tumor cell invasion in vitro correlated with lung colonization in vivo. Therefore, this model may provide a valuable tool to study the mechanisms involved in the pathogenesis of tumor cell invasion during hematogenous dissemination.