A crossbreeding experiment involving Baladi Saudi (S and While Leghorn (Ti chickens was carried out in El-Oassim region in Saudi Arabia to evaluate the growth performance and livability trails of the resulting crossbreds. Data of hi-weekly bot.o weights, daily gains in weight and livability were collected on 1281 chicks from the age of 0 to 12 weeks_ The genetic model of Dickerson was used to estimate the he:erotic components of this experiment in terms of heiero.sls (1-11) and direct (0 and maternal breed 011 additive cifccts. Chicks of L breed had superior performance in body weight. (1' 0.001) and daily gains in weight (F 0.01 or P 0.001) and livabilitr trails snulied compared to the S chicks.. Craning of S chickens with ones was associated with significant positive direct heterosis for some growth tram especially those weights and gains of early ages (0-6 weeks), while at later ages N-12 weeks, crossbred chickens recorded negative H for the same train. Heterotic effects decreased generally with advance of chick's age. The percentages ()fill ranged from 1.7 to 3.0%for body weights and gains at early ages of 0-6 weeks, while they ranged from -3.1 to 0.0% at later ages (6-12 Tivek.$). hi contras, 10 that.finmil in body weights cmd gains, estimates of 11-1 for livability were mostly negative during the early ages of 0-4 weeks, while ai later ages of 6-12 weeks they u 'ere positive and significant and ranged from 21? Ia 4.2%. 1 hider hot climatic conditions, additive maternity (Qt1) for studied trails was: generally significant and in favour of the S breed since chicks produced from LAS millings had better growth and livability traits