This study examined the in vitro cytotoxic activities of standardized aqueous bioactive extracts prepared from Coriolus versicolor and Funalia trogii ATCC 200800 on HeLa and fibroblast cell lines using a MTT (3-[4,5-dimetiltiazol-2-]-2-5-difeniltetrazolium bromide) cytotoxicity assay. F. trogii and C. versicolor extracts were cytotoxic to both cell lines. At 10 mu L treatment level, F. trogii and C. versicolor extracts inhibited proliferation of HeLa cancer cells by 71.5% and 45%, respectively, compared with controls. Toxicity was lower toward normal fibroblasts. In the latter case, treatment at 10 mu L level with F. trogii and C. versicolor extracts reduced cell proliferation by 51.3% and 38.7%, respectively. In separate experiments, the mitotic index (MI) obtained with 3 mu L treatment level of unheated extracts of the two fungi was comparable to the MI value obtained by treatment with 4 mu g/mL MMC (anticancer agent mitomycin-C). A significant induction of sister chromatid exchange (SCE) was observed in normal cultured lymphocytes treated with MMC (4 mu g/mL). MMC treatment reduced replication index compared with treatment with unheated F. trogii extract and negative controls (p 0.05). Laccase and peroxidase enzyme activities in F. trogii extract were implicated in their inhibitory effect on cancer cells. F. trogii extract was concluded to have antitumor activity.