Heat shock is considered an abiotic stress for plant growth. The effect of heat shock of various intensity on the leaves of the seedlings of the European beech (Fagus sylvatica L.) was studied. The seedlings were obtained from the seeds which were collected from different regions of the Republic of Moldova, Romania and Ukraine. The magnitude of the damage dealt to the photosynthetic apparatus was determined by the method of PAM - fluorimetry. The experiment was carried out during the period when 4–5 true leaves appeared in beech seedlings at a heat shock temperature of +50 and +52°C.