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.