The present study was carried out during 2001/2002, 2002/2003 and 2003/2004 seasons at the Experimental Farm of Faculty of Agriculture, Assiut University.  15 F₁'s obtained from a half diallel crossing system of six bread wheat parents were genetically analyzed to detect the type of gene action governing the heading date, yield and its attributes under favorable and stress conditions.  A Randomized Complete Block Design with three replications was adopted for each experiment.  Results showed that mean squares due to genotypes (i.e. parents and crosses) reached the significant level for all studied traits for both conditions as well as in the combined analysis.  Stress condition reduced number of days to heading, plant height, spike length, yield and its components as compared with non-stress condition.  The reductions in biological yield/plant from non-stress to stress as percentage were 19.98 and 29.19% for parents and F₁ generation, respectively.  Also, the reductions in grain yield/plant were 35.05% for parents and 32.25% for F₁. The calculated water stress susceptibility index (S) based on yield and its components revealed that the parental genotypes Giza 160, Sonora 64,  Leningradka and SAKHA 8 were relatively stress tolerant for no. of grain/spike.   The best crosses for grain yield/plant were (Giza 160 x Sonora 64), (Sonora 64 x Leningradka), (Giza 160 x Chenab 70) and (Leningradka x Chenab 70).                 Estimates of GCA effects revealed that the parental genotypes Sonora 64 and Sakha 8 seemed to be the best general combiners for earliness and Leningradka for grain yield/plant and yield components under both conditions.  The cross combinations (Leningradka x Sakha 8), (Sakha 8 x Chenab 70) and (Sonora 64 x Leningradka) showed high SCA effects for the mentioned traits.  The dominance gene effects accounted for the most part of the total variation for all traits except days to heading under favorable condition, resulting in (H₁/D)^1/2 more than one. Heritability estimates in broad sense were high for the studied traits except spike length in favorable (0.40) and number of grains/spike (0.49) in stress conditions.  Heritability values in narrow sense were low except for days to heading and ranged from 0.08 to 0.38.