In the 32-year-old mountain Norway spruce (Picea abies (L.) H. Karst.) forest in Bily Kriz Experimental Station in the Beskydy Mountains (Czech Republic), the influence of ozone stomatal flux on anatomical structure of needle and protective function of carotenoids were studied. The study focuses on the enlargement of intercellular space in mesophyll parenchyma after ozone exposure of trees. A relationship was found between enlargement of intercellular area in mesophyll and accumulated Phytotoxic Ozone Dose above a threshold of 1 nmol m^{-2} s^{-1} (POD_1). A ratio between intercellular and total area in mesophyll has been introduced as IM index. Protective function of carotenoids and, respectively, the dependence of the concentration of these pigments in P. abies needles on POD_1 index was proved.