In order to evaluate the effect of leaf age on enzymes of carbon and sulphur metabolism, chlorophyll (Chl) and protein contents and the activities of RuBP- carboxylase (RuBPC), ATP-sulphurylase (ATPS), and 0-acetylserinesulphydrylase (OASS) were determined in leaves of different ages from luceme (Medicago sativa L. cv. Lodi and Sewa) plants grown outdoors. The enzymes of sulphur and carbon metabolism were differently regulated throughout development of luceme leaves, as ATPS reached the highest activity at very early stages of leaf growth, when RuBPC activity was negligible. OASS activity inereased 2-fold during leaf expansion, and deereased with leaf senescence. The two cultivars showed rather similar trends of development in Chl, protein content and enzyme activities. The cultivars differed also in the absolute level of enzyme activities and other biochemical parameters.