SUMMARY - A total of 1058 animals from 23 different breed combinations (86% steers, 14% heifers) were slaughtered with an average age of 2½ years between 1996 and 2001. Heritabilities and genetic correlations were estimated for the following traits: weight at 12, 15 and 18 months of age, slaughter and carcass weights (hot carcass weight, pistola weight, valuable cuts weight), ribeye area, subcutaneous fat thickness and subcutaneous fat thickness at P8. The posterior mean of the heritability for live weights increases with age, from 0.33 at 12mo to 0.58 at the slaughter weight. The hot carcass weight had the highest posterior mean of 0.64 followed by the pistola weight (0.57) and valuable cuts weight (0.34). The lowest estimates of heritability were for the fat traits; 0.22 for subcutaneous fat thickness and 0.18 for fat thickness at P8. Hot carcass weight presented high genetic correlations (> 0.7) with the live weight traits, while the pistola weight and the valuable cuts weight had practically equivalent correlation estimates with the live weight traits (> 0.65). This is supported by the genetic correlations obtained between the hot carcass weight, the pistola cut weight and the valuable cuts weight, which were 0.94 to 0.96. These results determine the possibility of using live weight measurements as selection criteria to improve the hot carcass weight, so that the pistola cut weight and the valuable cuts will be improved. Likewise, the ribeye area would also be improved, while the subcutaneous fat thickness would not be substantially modified. This would not be an inconvenience at present, considering the data provided by the industry regarding adequatefat levels according to their demand, as well as the current conditions of production in the primary sector.