Highly aggressive cutaneous melanoma cells (upper panel) form patterned, tubular networks when cultured on three-dimensional collagen matrices. These networks, which mimic embryonic vasculogenic networks, contain MMPs-1, -2, -9 and MT1-MMP. A three-dimensional collagen matrix (lower panel) containing laminin tracks deposited by the highly aggressive melanoma cells, in cooperation with MMP secretion, can induce poorly aggressive melanoma cells (which do not form networks under normal conditions) to demonstrate vasculogenic mimicry when cultured on this aggressive cell conditioned matrix. For details, see the article by Seftor et al. on p. 6322 in this issue.