Essential Fatty Acids (EFA), are unsaturated fatty acids not produced by human being, but essential for proper functioning of the human body. To EFA-s belongs: linoleic acid (LA) (18:2,cis detla(9,12), omega6)--precursor o f gamma-linolenic acid (GLA), gamma-linolenic acid (GLA) (18:3,cisA6,9,12,)6) and alpha-linolenic acid (ALA)(18:3,cisdelta(9, 12, 15), omega3)--product of dehydrogenation of linoleic acid (LA). Most important EFA is gamma-linolenic acid (GLA)--18 carbons, one-carboxylic, non-branched fatty acid with 3 double cis-bonds (the last is situated by 6-th carbon from methylic end). The diet devoided of EFA leads to decreased growth, skin and kidney injury and infertility. Modern research of GLA and others EFA's is concerned mainly on therapeutic impact on the inflammatory process. The biogenic amines, cytokines, prostaglandins, tromboxanes and leukotrienes are the main inflammatory mediators. The last three are described with the common name eicosanoides (eico-twenty). Eicosanoides are synthesized from 20-carbon unsaturated fatty acids: dihomo-gamma-linoleic (DGLA) (20:3, cis delta(8,11,14), omega6), arachidonic acid (AA-20:4, cis delta(5,8,11,14), omega6), and eicosapentaenoic acid (EPA-20:5, cis delta(5,8,11,14,17, omega3). Derivatives of gamma and gamma-linolenic acids regulate the inflammatory process, through their opposed activity. PG2, leucotrien C4 and tromboxan A2 have the strongest proinflammatory action. Derivatives of alpha-linolenic acid 15-HETE and prostaglandin E1 (PGE1) have weak pro-inflammatory action, or even anti-inflammatory (PGE1), and additionally, they inhibit the transformation of arachidonic acid (AA) to leukotriens. delta6-desaturase (transformes linolenic acid into gamma-linolenic acid by making additional double bond) is the slowest step of the fatty acid metabolism. It's activity is impaired by many physiological and pathologic factors and leads to gamma-linolenic acid (GLA) deficiency. The gamma-linolenic acid supplementation in diet allows to omitt the inefficient delta6-desaturase system which has an effect in rising of dihomo-gamma-linolenic acid (DGLA), arachidonic acid (AA) and their derivatives. This article describes biology of essential fatty acids and particularly the role of gamma-linolenic acid.