Tumor cell attachment to endothelial cells (EC) is one of the critical steps of the metastatic process. It was previously reported that interleukin 1 treatment of EC induces expression of membrane molecules that promote tumor cell adhesion. In this paper we report that a panel of six clones isolated from a human metastatic melanoma presented a marked heterogeneity in their ability to adhere to interleukin 1 activated EC. This was correlated with integrin VLA-4 expression by the clones. Antibodies directed to VLA-4 and to its endothelial ligand INCAM110/VCAM-1 abolished interleukin 1 induced increase in melanoma cell adhesion to EC. These data demonstrate intratumor heterogeneity in the expression of VLA-4 and that this can represent a crucial determinant of tumor cell interaction with EC during secondary spread.