The additive and additive-by-additive genetic variance components of productive traits in two strains of laying hens were estimated. A total of 8035 individuals (base and recorded) from eleven generations were included in the analysis. Body weight, age at sexual maturity, average egg weight and initial egg production were considered. Before the estimation of the variance component, modeling of fixed effects (generation and hatch period) and covariables were performed. The data were transformed by use of the Box-Cox method. The DFREML algorithm under a single trait animal model was employed. It was concluded that additive-by-additive epistasis effects are not important for the studied performance traits. The results also indicate that deviations from normality influence the magnitude of variance component estimates in a highly indirect manner. This leads to an increase of heritability estimates.