The effect of 3-methylcholanthrene (3-MC), an inducer of the mixed function oxidases system (MFOS), was investigated in male Wistar rats in relation to plasmatic cholesterol and hepatic glucose-6-phosphate dehydrogenase (G-6-PD). 3-MC induced an increase in total cholesterol; the maximal increase was seen 2 days after treatment (50%). The increase in total cholesterol was followed by an augmentation in cholesterol HDL. 3-MC treatment resulted also in an increase of hepatic G-6-PD.