The invention is based on the discovery that angiogenic vessels have heterogeneous surface charge and that cationic liposomes actually target human tumor blood vessels only in irregularly shaped patches. The invention thus features methods for delivering therapeutic compounds to angiogenic vascular endothelial surfaces using a mixture, or “cocktail”, of positively charged and neutral liposomes. The new methods can be used to target multiple regions on the same tumor vessel and/or clusters of vessels within the same tumor. Liposomes with different chemical and/or physical properties (e.g., charge, stability, solubility, diameter) can be delivered simultaneously, and can target tumor vessels and other angiogenic vessels with greater efficiency compared to cationic liposomes alone.