The main purpose of this work was to compare two breeds of improved rams (Suffolk and Merino Precoce) with the local Galego Bragangano breed for the production of crossbred slaughter lambs and to evaluate which cross was more adapted for meat production from the local breed in locations in the north-east of Portugal. The experiment was carried out over a 4-year period in three locations: (1) a farm with an intensive management; (2) an upland farm (400 to 600 m); and (3) a hill farm (above 800 m). Within each flock with 90 Galego Bragangano ewes, two rams of each of the sire breeds were used: Galego Bragangano, Suffolk and Merino Precoce. The lambs were slaughtered at 20 and 40kg, to obtain the carcass weight range of 8 to 14kg. The left sides of 151 carcasses were dissected into muscle, subcutaneous fat, intermuscular fat and bone. The lambs from location 1 had the highest carcass muscle proportion and the lowest carcass intermuscular fat proportion; their differences over locations 2 and 3 were 13 and 16 g/kgfor muscle proportion and 11 and 19 g/kgfor intermuscular fat proportion, respectively. The differences between breeds were relatively small and not significant. However the Suffolk crosses had less kidney, knob and channel fat than the other genotypes (5 and Uglkg less than Merino crosses and Bragangano, respectively). The Suffolk crosses tended to have less body fat.