Degradation of methyl mercury by mink was investigated in a series of experiments. Mink were fed daily with a diet containing methyl mercury-contaminated fish. Contents of total mercury, methyl mercury and selenium were determined in different tissues from the animals, as were the contents in faeces. Of the total amount of mercury detected, only about 73% was found as methyl mercury. In liver and kidney the proportions were 46 and 55%, respectively. Selenium contents were low compared with those found in marine mammals where equivalent amounts of mercury and selenium on a molar basis have been reported. The conditions in mink are compared with earlier studies on cats and marine mammals.