The mutagenicities and antimutagenicities of butanol (PL I) and water (PL II) extracts from the filtrate of the cultured broth of Phellinus linteus were examined using the Ames/Salmonella test. No mutagenic activity of PL I and PL II was found in Salmonella typhimurium strains TA98 and TA100, either with or without S9 activation. In contrast, PL I and PL II showed inhibitory effects on the mutagenic activities induced by the directly-acting mutagens, 4-nitro-o-phenylenediamine (NPD) using the tester strain TA98 and sodium azide (NaN3) using the tester strain TA 100 in the absence of S9 mix. PLI and PL II also showed inhibitory effects on the mutagenicities of the indirectly-acting mutagens, 2-aminofluorene (2-AF) using the tester strain TA98 and benzo[a]pyrene (B[a]P) using the tester strain TA 100 in the presence of S9. These results suggest that P. linteus has an antimutagenic activity and may play a role in the prevention of cancer.