The biotransformation of etheofazine (EDMTP), a new anticancer drug, was studied by using isolated perfused rat liver. Two main metabolites were separated from the perfusate by HPLC and TLC and their chemical structures were determined by MS, 1H-NMR and IR. EDMTP-I is the parent compound. EDMTP-II is 7-ethyl-8-aminotheophylline. EDMTP-II was also separated and identified from the blood of mice after iv of 10 mg/kg. Species difference of biotransformation of EDMTP between rat and mouse seems to be not significant in this study.