Cover photograph (Copyright © 2000, American Society for Microbiology. All rights reserved.): Depicted is a whole mount of a murine tumor derived from cells which are nullizygous for the angiogenic protein vascular endothelial growth factor (VEGF); in these cells, specific expression of one VEGF isoform, VEGF120, has been reintroduced via stable transfection. The vasculature of the tumor was visualized by perfusion with a yellow latex compound, followed by clearing of the excised tumor with glycerol. This demonstrates that specific expression of this isoform in isolation from others results in tumors successful in recruiting peripheral vasculature from the host but deficient in internal capillarization. (See related article on p. 7282.)