A datafile of 1917 weigth records of 579 animals from the 16 possible crosses among 4 strains of iberian pigs was analyzed in order to estimate crossbreeding parameters for two growth traits: weigth at 14 m. (P_14M) and average daily gain during the final fattening (GMD). A fixed model was compared with a bivariant animal model solved using three alternative methods: restricted maximum likelihood and a bayesian analysis of intercept and slope of linear growth function including or not a priori information about (co)variance components. The standard errors of the estimated parameters are underestimated with the fixed model and increase with the uncertainty of the variance components. The most efficient use of data allowed by the bayesian techniques also contributes to modify the inferences about some parameters according the used procedure. The results show a significant mean heterosis for both traits with values, expressed as percentage of the average of the pure strains, ranging from 9.8 to 16% (P_14M) and from 5.5 to 10% (GMD). These values validate the interest of the crossbreeding between lines as a useful tool to improve growth rates in the final fattening of Iberian pigs.