(abstract P4). Influence of phenolic acids on oxidative metabolism in liver mitochondria (a), tissue homogenates (b) and removing their inhibitory effect by N-acetylcysteine (c). Optical density of reduced NBT in the presence of 5 mM substrate and 100 μM phenolic acid – benzoic (BZ), phenyllactic (PL), p-hydroxyphenyllactic (HPL), phenylacetic (PA), p-hydroxyphenylacetic and phenylpropionic (PP) acids is presented. Inhibitors of NAD-dependent oxidation rotenone and N-ethylmaleimide (NEM) confirm the substrate specificity of NBT reduction. Antioxidant N-acetylcysteine (1 mM) prevents the inhibition induced by phenolic acids. * р < 0,05 compared with the corresponding control.