Analogs of combretastatin have been discovered which demonstrate impressive cytotoxicity as well as a remarkable ability to inhibit tubulin polymerization. Such compounds are excellent clinical candidates for the treatment of cancer in humans. In addition, certain of these ligands, as pro-drugs, may well prove to be tumor selective vascular targeting chemotherapeutic agents or to have vascular targeting activity resulting in the selective prevention and/or destruction of nonmalignant proliferating vasculature.