The work was performed in order to evaluate possible negative effect of high temperatures on biological properties of seeds in space experiment BIORISK-MSN-2. Laboratory experiments showed that seeds possess high enough resistance to extended exposure to high temperatures. Results of studying effects of positive temperatures in the region of 40 to 100 degrees C on biological properties of seeds of 19 species and varieties of higher plants belonging to three different families lead to the conclusion that heat stability of seeds depends on temperature value, period of exposure, species, variety and individual peculiarities of plants. These data can be useful in future interpretation of results of experiment BIORISK-MSN-2.