The influence of dietary essential fatty acids on the immune functions and nonspecific resistance of male Wistar rats weighing 135.0 +/- 3.2 g was investigated after 3 months feeding. Rats were fed isocaloric purified diets containing 24% of fat (combinations of lard, sunflower oil and fish oil, eiconol, this providing the ratios of omega 6/omega 3 fatty acids equal to 1.1; 2.1; 6.1; and 49.0. An increase of immune responsiveness and nonspecific resistance in the groups fed diets with the minimal ratios of omega 6/omega 3 fatty acids as compared to that in rats fed a diet with ratio 49.0 was noted. Fatty acid analysis of peripheral lymphoid organs tissue lipids showed an increase in percentage of eicosenic omega 3 fatty acids in rats fed diets with increased content of polyunsaturated fatty acids omega 3.