In the present study, the heat acclimation processes (growing at 30/27°C for 2 weeks) in spring and winter varieties of barley (Hordeum vulgare L., varieties ‘Conchita’ and ‘Mv Initium’) and oat (Avena sativa L., varieties ‘Mv Pehely’ and ‘Mv Hópehely’) were characterized. Temperature dependence of certain chlorophyll a fluorescence induction parameters indicated the efficiency of heat acclimation. Heat treatment induced the activity of glutathinone-S-transferase, but decreased the amounts of the major polyamines. A significant increase in cadaverine content was found in ‘Conchita’. 1,3-diaminopropane contents after heat acclimation were lower in the oat and higher in the barley varieties than that in the control plants. Salicylic acid and para-hydroxybenzoic acid contents were also induced at elevated temperatures. Changes in abscisic acid differed in the two species. Results suggest that besides certain similarities, different strategies can be activated to avoid the damaging effects of high temperatures in barley and oat plants.