Methods of treating tumors in a mammal, especially a human that has demonstrated resistance to other chemotherapeutic agents, is disclosed. Specifically, methods of the present invention are effective in tumors that have initially been unresponsive to taxane therapy, or have developed resistance during the course of treatment. The methods of the present invention comprise administering epothilone derivatives selected from those represented by the formula: ##STR00001## The subject epothilone derivatives are advantageous in addition to their enhanced potency and effectiveness against tumors that have demonstrated resistance to therapy with taxane oncology agents in that they are efficacious upon oral administration.