Summary. The metabolism of testosterone and 4-androstene-3,17-dione was studied in rat liver preparations after a single injection of carbon tetrachloride or phalloidin respectively and after oral administration of ethanol. The following results were obtained:After carbon tetrachloride and phalloidin the reduction rate of both steroids decreased rapidly (p < 0.001) in liver tissue sections as well as in microsomal preparations containing a NADP-regenerating system. It is therefore concluded, that this is a direct effect on the enzyme protein of the 4,5-dihydrosteroid:/qADPoxidoreductase.After ethanol the reduction capacity is also significantly (p < 0.001) depressed but it becomes normal if ethanol administration is stopped. Under special conditions with the NADP-regenerating system added to the microsomal preparation no depression of the reduction capacity is seen. In this case it is assumed that the depression of reduction rate is caused by a lack of coenzyme and is reversible.

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