The developmentally-dependent differences in the biological significances and effects of PUFA-OMEGA-6 (namely of arachidonic acid) and PUFA-OMEGA-3 (namely of docosahexaenoic acid) are discussed. The clinical results as well as developmental experiences are indicating a hypothesis of the evolution that created mutual relationship between those two substances (with immunological basis and following recuperation). The anti-inflammatory actions of PUFA-OMEGA-3 are the most visible (and significant) contrasts as compared with the large affects of namely arachidonic acid and its metabolites.