The influence of higher temperatures on the polypeptide composition of thylakoid membranes and pigment-protein complexes, as well as on some parameters of their functional activity, in both acclimated and non-acclimated young pea plants, was studied. Almost the whole set of polypeptides in thylakoid membranes as vvell as in T40 particles was preserved after heat treatment (5 h, 55 °C). During acclimation of the plants to high temperatures a reorganization of the photosynthetic apparatus took plače. In its thylakoids the oligomer/monomer ratio of the photosystem (PS) 2 light- harvesting antenna was more than 50 % higher compared to similar samples of the non-acclimated plants. After both the treatment of 5 h at 55 °C only (non-acclimated plants) and that with step-wise increasing temperatures (acclimated plants), the PSI activity was practically unchanged in all three variants, whereas the PS2 activity decreased more significantly in non-acclimated plants only.