A survey of litter samples from broiler houses at widespread localities in the U.K. revealed a significant difference between the fungal floras before and after the houses had been used for a single crop of birds. Paecilomyces varioti, Trichoderma spp. Aureobusidium pullulans, and Hyalodendron lignicola predominated in the fresh litter, but were replaced by Scopulariopsis brevicaulis and Aspergillus spp. in the final samples. The fungi present in the final litter samples were also found in the initial and final dust samples, indicating that the dust is a potential source of inoculum. These results are discussed in relation to the formation in broilerhouse litter of 2,3,4,6-tetrachloroanisole (a compound associated with a musty taint in chickens), and to the potential formation of mycotoxins.