The antimutagenic effects of uninoculated milk and milks cultured with Bifidobacterium or Lactobacillus strains towards the mutagenicity induced by two direct mutagens, 4-nitroquinoline N-oxide and 2-nitrofluorene, and three dietary indirect mutagens, aflatoxin B1, benzo(a)pyrene and quercetin, were investigated using the in vitro Salmonella typhimurium test. Each cultured milk sample and control milk had a significant antimutagenic effect, to an extent varying with the mutagen used. Uninoculated milk had a greater inhibitory effect than cultured milks towards dietary indirect mutagens.