The cause and origin of musty taint in chicken from broiler systems has been established as 2,3,4,6-tetrachloroanisole formed by microbial methylation of 2,3,4,6-tetrachlorophenol present as a wood preservative on shavings used as litter. At least three of the fungi found in poultry litter (Scopulariopsis breuicaulis, Aspergillus sydowi and Penicillium crustosum) can effect this methylation. 2,3,4,6-Tetrachloroanisole formed in the litter was taken up by the chickens. The levels in various chicken tissues and factors affecting uptake and loss have been investigated.