1. Mice when fed a cholesterol/choline-supplemented diet for 4 weeks developed histologically fatty livers. This lipid overloading was associated with an increase in hepatic concentration of connective tissues. 2. Both histological and biochemical abnormalities regressed on stopping the cholesterol diet for another 4 weeks. With continuing feeding for 24 weeks these abnormalities were sustained. 3. In the absence of available evidence that cholesterol is 'toxic' to the liver, it is concluded that lipid loading alone increases hepatic fibrogenesis.