Heat temperature is a limiting factor for plant growth, but some plants are able to acclimate showing a marked heat resistance. Pea seedlings {Pisum sativum L.) cv. Pleven 10 (winter cv.) and Auralia (spring cv.) grown in hydroponie cultures were heat acclimated at 40, 45 and 50 °C. Non-acclimated and acclimated plants were subjected to heat stress at 55 °C and in isolated thylakoid membranes fatty acid composition and changes in the main lipid classes (monogalactosyldiacylglycerols, digalactosyldiacylglycerols and phospholipids) were determined. The acelimation to heat lead to some resistance towards heat stress, and was more expressed in the cv. Auralia.