Abstract A study has been made of the changes in the concentration of HEOD in four tissues of male rats during a 12-wk period on a basic diet, following consumption of a diet containing 10 ppm HEOD for 8 wk. Empirical relationships, containing one exponential term in the case of the adipose tissue and brain, and two exponential terms in the case of blood and liver, have been fitted to the results. The half-lives of HEOD in the liver were estimated to be 1·3 and 10·2 days for the rapid and slower periods of elimination, respectively, and similar values were estimated for the blood. The estimated half-lives for the adipose tissue and brain were 10·3 and 3·0 days, respectively. The order of storage in the four tissues was: adipose tissue ≫liver > brain > blood. The equations have been discussed in relation to a simple pharmacokinetic model and it is concluded that the elimination of HEOD from the rat may be simulated by a model containing two compartments.