Effect of short term administration of dibutylhydroxytoluene (BHT) on lipids and drug metabolizing enzyme system of liver in female rats were investigated. 1) BHT administration caused liver enlargement and the increase of cholesterol in microsomes and mitochondria, and that of phospholipid in microsomes, but no change in serum cholesterol, liver glycogen and triglyceride contents. 2) BHT administration did not change the percentage composition of phospholipids. However, BHT administration

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... ased the percentage of stearic acid in mitochondria phosphatidyl ethanolamine and phosphatidyl choline fractions, while it decreased that of unsaturated fatty acid such as arachidonic acid. 3) The activity of aminopyrine demethylase, the contents of cytochrome P-450 and b5, and the spectral difference of aniline binding increased significantly by the BHT administration.