A large number of active principles from traditional medicinal plants have been reported to have chemopreventive properties. In the present study, therapeutic efficacy of an aqueous extract of Indigofera aspalathoides against growth of transplanted experimental fibrosarcomas in Wistar strain male albino rats was tested. Tumors which appeared about six weeks after implantation were highly localized and were maintained by serial transplantation. Rats were divided into four groups. Group I served as normal control animals. Group II were fibrosarcoma bearing animals. Group III were animals with fibrosarcoma treated with Indigofera aspalathoides aqueous extracts at a dose of 250 mg/kg. b. w. per day for 30 days. Group IV animals were treated with aqueous extract of Indigofera aspalathoides alone. Reduction in tumor weight was noted in Group III as compared to II. The levels of cytochrome C in liver and kidney, the levels of cytochrome P450 and cytochrome b5 in liver microsomes, phase I biotransformation enzymes NADPH-cytochrome P450, NADPH-cytochrome b5, and aniline hydroxylase, and the phase II enzymes glutathione-S-transferase and UDP glucuronyl transferase indicated that their modulation played a role in the therapeutic efficacy of Indigofera aspalathoides against experimental fibrosarcoma.