Immunofluorescent staining of M21 human melanoma tumors treated with partially inactivated PAI-1 demonstrates a highly branched network of vessels surrounding tumor nodules. The endothelial cells are red, vitronectin in the extracellular matrix is green, and the tumor cells are blue. McMahon, et al., pages 33964-33968, show that in comparison fully active PAI-1-treated tumors show significantly fewer branch points, suggesting that increasing concentrations of PAI-1 may significantly affect angiogenesis.33964.