Four experiments were conducted in 1997 and 1998 in two contrasting environments (irrigated and rainfed) in north-eastern Spain. Each experiment included 25 durum wheat genotypes grown in the Mediterranean region. Canopy temperature depression (CTD) from the air was determined at anthesis and milk-grain stage. Stable carbon isotope discrimination (D) and nitrogen (N) content were further determined in mature grains. Genotypical effects accounted for a small part of the variability found in all the traits. The year effect was very important to explain CTD differences at anthesis and N content of grains. Differences between the irrigated and the rainfed environment accounted for most of the variability found in yield and D, and were also important to explain differences in N. Broad sense heritabilities were higher for D and N than for grain yield, and were very low for CTD both at anthesis and at milk-grain stage. Carbon isotope discrimination was the trait most related to grain yield, the coefficient of correlation increasing from the worst (i.e. rainfed) to the best (i.e. irrigation) trials.