The anticancer activity of dichloromethane extract of guduchi [Tinospora cordifolia (WILLD.) MIERS ex HOOK. F. & THOMS. Family: Menispermaceae (TCE)] in the mice transplanted with Ehrlich ascites carcinoma (EAC) was investigated. The EAC mice receiving 25, 30, 40, 50 and 100 mg/kg, TCE showed a dose dependent elevation in tumor-free survival and a highest number of survivors were observed at 50 mg/kg TCE, which was considered as an optimum dose for its neoplastic action. The average survival time (AST) and median survival time (MST) for this dose were approximately 56 and 55 d, respectively when compared with 19 d of non-drug treated controls. Administration of 50 mg/kg TCE resulted in 100% long-term survivors (up to 90 d). An attempt was also made to evaluate the effectiveness of TCE in the various stages of tumor development, where 50 mg/kg TCE was administered intraperitoneally after 1, 3, 6, 9, 12 or 15 d of tumor inoculation and these days have been arbitrarily designated as stage I, II, III, IV or V, respectively for reasons of clarity. The greatest anticancer activity was recorded for stage I, II and III where number of long term survivors (LTS) was approximately 33, 25 and 17%, respectively. However, treatment of mice at stage IV and V did not increase LTS, despite an increase in AST and MST. The EAC mice receiving 50 mg/kg TCE showed a time dependent depletion in the glutathione (GSH) activity up to 12 h post-treatment and marginal elevation thereafter. This depletion in GSH was accompanied by a drastic elevation in lipid peroxidation (LPx) and a maximum elevation in LPx was observed at 6 h that declined gradually thereafter. TCE exerted cytotoxic effect on tumor cells by reducing the GSH concentration and increase in LPx simultaneously.