The rate of phosphoenolpyruvate carboxylation by extracts from germinating lupin seeds was measured through the H¹⁴CO₃ fixation. PEP carboxylation in seed axes increased during their imbibition, mainly as a result of the increase in the activity of PEP carboxylase [EC 4.1.1.31]. However, the activity of PEP carboxykinase [EC 4.1.1.38], present during the first 3 hours of imbibition, as well as the activity of PEP-carboxykinase [EC 4.1.1.49], after 24 hours of imbibition, have also been shown. Possible physiological role of the changes in the activity of PEP carboxylases during lupin seeds germination is discussed.