The VLA3 (alpha 3 beta 1) integrin receptor recognizes several ligands; however, the function of this integrin is still debated. Expression of VLA3 appears to be increased in malignant melanoma and correlates with the degree of dermal invasiveness. Here we have studied the role the alpha 3 integrin subunit in malignant melanoma cell migration and invasion into extracellular matrices. The 2/14 clone of the Me665/2 human melanoma cell line, which expresses high levels of VLA integrins, was highly migratory and invasive, while the low integrin expressing 2/56 clone showed limited migration and was not invasive. Antibodies to the beta 1 subunit inhibited adhesion, migration, and invasion of two different malignant melanoma cell lines, the 2/14 clone and A2058 cells, indicating a crucial role for VLA integrins in these phenomena. While anti-alpha 6 antibodies inhibited adhesion to laminin and anti-alpha 5 antibodies inhibited adhesion to fibronectin, antibodies to the alpha 3 subunit did not inhibit adhesion of these cells to laminin, fibronectin, or collagen i.v. In contrast, the P1B5 anti-alpha 3 antibodies were good inhibitors of the migration of these cells toward laminin, fibronectin, and collagen IV and also blocked invasion of these cells through a reconstituted basement membrane matrix (Matrigel). Another anti-alpha 3 antibody, F4, did not effect migration, while both the P1B5 and F4 antibodies induced cellular aggregation on Matrigel. Our data suggest a specific role for alpha 3 beta 1 in the migration and invasion of melanoma cells.