Growing interest in the role of dietary fat in the development of chronic disease has stimulated debate concerning the potential benefits of modifying the fatty acid composition of animal products. The use of various dietary fat sources in animal feeding to manipulate polyunsaturated fatty acids (both the ω-6 series and ω-3 series) and the monounsaturated fatty acid composition of animal products is reviewed, by Miss Van Elswyk, who received the 1992 Williams & Wilkins gradaute student first-place award.