The three main objectives of the present study, carried out in durum wheat grown in the high-plains of Sétif (Algeria) were i) to examine the genotype x environment interactions for grain yield, ii) to analyse the relationship between yield and the carbon isotope discrimination (D) of grain and different organs (flag leaf, peduncle, rachis and awns) and iii) to study the contribution of these organs to the grain filling. The usefulness of D analysis in breeding programs and interest of performing it in different organs for a better understanding of their contribution are discussed.