Tumor cell interaction with the extracellular matrix is defined as the critical event of tumor invasion that signals the initiation of a metastatic cascade. Sesquicillin has been identified as an inhibitor of melanoma cell adhesion to the components of the extracellular matrix (ECM) in cultured broth of fungal strain F60063. Sesquicillin strongly inhibited the adhesion of B16 melanoma cells to laminin, fibronectin, and typeIV collagen. It also inhibited B16 melanoma cell invasion of reconstituted basement membrane Matrigel in vitro in a dose-dependent manner. These results suggest that sesquicillin is a new class of nonpeptidic ECM adhesion inhibitor having anti-invasive activity.