Gas chromatography (GC) has been an indispensable analytical technique ever since the first exciting steps in the application of fatty acid determinations in oilseed plant breeding, biosynthesis and human metabolism. Present-day GC methods with high-quality capillary columns allow sensitive and reproducible fatty acid analyses, as well as the characterization of complex mixtures of geometric isomers when combined with other chromatographic separations and spectroscopic identification. Ordinary GC analysis is well suited for a detailed follow-up of the changes in human tissue fatty acids derived from dietary fats providing, however, that all the steps in the methodology are carefully optimized. Plasma fatty acids act as excellent indicators, and the use of substitute fats can be found as dose-dependent correlations. Analysis of phospholipid (PL) fatty acid composition is especially useful for recognizing the competitive capability of essential fatty acids present in a particular dietary fat. A clear response is observed even at the level of minor fatty acids, i.e. both increased and decreased use of trans fatty acids are indicated by changes in the most abundant octadecenoic trans isomers. In addition to the expected associations with serum lipids, plasma fatty acid data are also useful in monitoring relationships with lipid oxidation parameters. GC analysis of fatty acids still has its traditional uses, but it is now faced with new challenges. Since the effects that arise from even moderate amounts of dietary essential fatty acids cannot be neglected, continuing research aimed at their requirements is of prime importance. Modification of fatty acid compositions by metabolic engineering offers good possibilities for producing new oilseed crops with a more balanced alpha-linolenic/linoleic acid (LA) ratio, preferably combined with a high oleic acid (OA) content. In the future, particular attention has to be paid to the proportions of polyunsaturated fatty acids (PUFAs) in the diet, which are the factors that finally determine the apparently unique balance of tissue n - 3 and n - 6 fatty acids and eicosanoids decisive for human health. (C) 2002 Elsevier Science B.V. All rights reserved.