Cooking fats from a pressure deep-fat frying operation producing fried chicken, were compared with laboratory heated and fresh fats in the diets of animals. Included were corn oil (CO), peanut oil (PO), and partially hydrogenated soybean oil (HSBO). Weanling rats were fed diets containing 15% fat for 28 days. Laboratory heating reduced absorption of CO and PO, but not that of HSBO. Pressure deep-frying increased absorption of HSBO. Animals derived less metabolizable energy from diets containing heated or hydrogenated fats relative to fresh oil. Polar lipid fractions of liver changed due to heating. Pressure deep-frying with fats resulted in less deterioration than with laboratory heating, as shown by chemical analyses, coefficient of digestibility, and metabolizable energy studies.