In this study, carcass performance from data on 371 steers produced in a four-breed diallel crossing design was evaluated, Steers of the z Angus, Brown Swiss Hereford, Holstein breeds and all possible two-breed combifations were slaughtered at an average age of 14 mo Based on breed effects from the analyses of variance, the dairy (Holstein and Brown Swiss) had heavier slaughter and carcass weights and less external fat than the beef (Angus and Hereford) breeds The Brown Swiss breed had the largest longissimus muscle area, the highest estimated cutability percentage and the lowest marbling scores and quality grades of the four breeds. The Angus breed had the highest marbling scores and quality grades. The Hereford breed had the lowest estimated kidney fat percentage of the four The Holstein breed did not differ from the Hereford breed for marbling score and quality grade. Significant average heterosis was found for slaughter weight, carcass weight, longissimus muscle area estimated kidney fat percentage, marbling score and quality grade. Beef x dairy crosses ex hibited heterosis for marbling score and quality grade, whereas Angus Hereford and Holstein