A large intercross between the domestic White Leghorn chicken and the wildancestor, the red junglefowl, has been used in a Quantitative Trait Loci (QTL)study of growth and egg production. The linkage map based on 105 marker loci wasin good agreement with the chicken consensus map. The growth of the 851 F2individuals was lower than both parental lines prior to 46 days of age andintermediate to the two parental lines thereafter. The QTL analysis of growthtraits revealed 13 loci that showed genome-wide significance. The four majorgrowth QTLs explained 50 and 80% of the difference in adult body weight betweenthe founder populations for females and males, respectively. A major QTL forgrowth, located on chromosome 1 appears to have pleiotropic effects on feedconsumption, egg production and behaviour. There was a strong positivecorrelation between adult body weight and average egg weight. However, threeQTLs affecting average egg weight but not body weight were identified. Aninteresting observation was that the estimated effects for the four major growthQTLs all indicated a codominant inheritance.