It has been previously reported that Polifat KA-02 (fatty acids derived from safflower oil) prevents the pigment cholelithiasis produced by vitamin A in the golden hamster. In order to establish whether the saturation or the unsaturation of Polifat is directly related with its preventive action, in the present study the effect of the hydrogenation of the derivative on this preventive action was tested. Two experiments were carried out in which the animals received the different experimental diets ad libitum during 70 days. In the 1st. experiment the effect of the additions to the lithogenic diet (Rodents Chow + 25,000 UI% of retinol acetate) of 18% of crude safflower oil, or 15% Polifat, or 15% hydrogenated Polifat (approx. 80% saturation) were assayed. In the 2nd. experiment the effect of a more hydrogenated Polifat KA-02 (greater than 99%) was tested. The results of the 1st. experiment showed that the lithogenic diet produced a high incidence (90.5%) of animals with gallstones, which was very similar (100%) to that produced by the crude safflower oil, whereas the additions of normal and hydrogenated Polifat completely prevented the formation of gallstones. The 2 forms of Polifat produced a considerable hepatomegaly. The absorption of vitamin A, measured as total hepatic vitamin A, was higher in the 3 groups that received extra lipids in their diets. The results of the 2nd. experiment fully confirmed the findings related to the hydrogenated Polifat. It is concluded that hydrogenated Polifat KA-02 prevents, as normal Polifat does it, the pigment cholelithiasis in the golden hamster produced by vitamin A.