1. Three pure breeds, Aberdeen-Angus (AA), Ayrshire (AYR) and British Friesian (FR), and three crossbreds, Aberdeen-Angus × Ayrshire (AA × AYR), Aberdeen-Angus × British Friesian (AA × FR) and British Friesian × Ayrshire (FR × AYR) were studied. Each breed type was represented by 12 male castrates which were the progeny of at least seven sires in each case. 2. The purebred cattle of dairy type (FR and AYR) were faster growing (P < 0·001), heavier at slaughter (P < 0·001) and produced heavier carcasses (P < 0·001) than the pure beef breed. There were no significant differences between the breeds in the lean contents of their carcasses and there was no indication of any systematic breed effect on the distribution of lean within the carcass. The AA had carcasses with a higher fat content (P < 0·05), a lower bone content (P < 0·001) and a higher lean:bone ratio (P < 0·001) than the FR and AYR. 3. In general the values for performance and carcass data of the crosses between the three purebreeds fall mid-way between their parent values or do not differ significantly from this value. The hypothesis that crossbred cattle produce carcasses with higher muscle: bone ratios than purebred cattle is refuted by these data.