The aim of the study was to investigate the level of essential polyunsaturated fatty acids (PUFAs) in athletes into the training period and after endurance race (n=15 high-trained male cross-country skiers, real members of national skiing team). The PUFAs in plasma was determined by the gas-liquid chromatography method. Results demonstrate a deficiency of plasma level of the n-3 PUFA of the almost all skiers during the training period. Competition activity modified the essential PUFA profile in blood across more twice increase of the n-3 docosahexaenoic acids (DHA) (p=0.112) and n-3 alpha-linolenic (ALA) (p=0.048) levels and decrease n-6 PUFA relative to baselines, which expressed in a decrease in n6/n3 ratio (p=0.017). Relationships between n3/n-6 ratio and base heart rate, diastolic pressure and Maximal oxygen uptake, show on the significant role essential PUFAs in regulation of the cardiovascular system in cross-country skiers.