SUMMARY1A muddy or “earthy” taste can be imparted to the flesh of trout by material produced by an odoriferousActinomyces.2The taste resembles that imparted by a natural mud rich in actinomycetes.3The taint appears to be acquired through the gills and to be carried in the blood stream.4The taint can be slowly removed by clean flowing water.The authors wish to express their thanks to the Director of Fishery Investigations of the Ministry of Agriculture and Fisheries for permission to publish these results, and to the Inspector of Salmon Fisheries for Scotland for his interest in the work. Acknowledgment is also due to the Director of Chemical Research in the Department of Scientific and Industrial Research for facilities afforded in publication of the results of these experiments with which the Water Pollution Research Board of the Department has also been concer