Relationships of CTD (Canopy Temperarture Depression) with grain yield and its components were evaluated under Cukurnova conditions, Turkey, in 2003 growth season. With this aim, six bread and five durum wheat genotypes were used as a material. CTD was measured three times during beginning of heading to full anthesis stages and only at the last measurements, both bread wheat and different wheat genotypes showed significant differences. At the last measurements, CTD of bread wheat ranged between -0.22 and 0.57 degrees C. On the other hand, CTD average values of durum wheat genotypes changed 0.63 to 1.23 degrees C. This study showed chat durum wheat was cooler than bread wheat in high temperature conditions. In addition, CTD was positively correlated with grain yield, spike yield, and grain numbers per spike, Overall, CTD has played an important role to search physiological basis of grain yield of wheat, and CTD can successfully use as a selection criterion in breeding programs.