Genetic variability of leaf net photosynthesis rate (A(n)) and its relation to productivity in durum wheat (Triticum turgidum L. var. durum) is not well defined. Two field experiments were conducted at the experimental area of the Faculty of Agriculture, in the University of Cukurova, Turkey, to evaluate the differences between old and modern cultivars in A(n) and productivity. Experiments with sowing dates in November 1996 and February 1997 were performed under rainfed and irrigated conditions, respectively. Measurements included leaf gas exchange and agronomic traits. Old cultivars (OC) were later flowering and taller than modern cultivars (MC) and their harvest indexes were lower. Before the onset of leaf senescence, most of the OC exhibited higher A(n) values than most of the MC, but the extent of variability was not great. High A(n) was correlated with high stomatal conductance (g(s)), but no overall correlation between A(n) and the ratio of internal [CO2] to [CO2] in the air was observed. In spite of higher A(n), OC showed no superiority in grain yield. The results indicate that mesophyll conductance rather than g(s) has an effect on variation in A(n), and that preanthesis dry matter distribution and total flag leaf photosynthesis and its duration appear to be more relevant than A. for grain yield, especially under drought.