Novel polythiophene compounds useful as anti-tumor agents are described. Preferred compounds of formula (I) wherein n is 0-2 and R2 and R3 are optionally substituted 2-thienyl or 3-thienyl have been found to exhibit selective cytotoxic activity against transformed human cells. Pharmaceutical compositions containing the described polythiophene compounds are expected to exhibit good chemotherapeutic activity against slow growing tumors based on tumor cell line assays. A method for treating patients having tumors utilizing the disclosed polythiophene compounds is also described.