Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) ; The objective of this work was to compare the growth and chemical composition of the main body parts of males and females of the Ross and Cobb broiler strains available in Brazil. In total, 1,920 chicks were raised in 16 floor pens, from which 4 birds of each strain and sex were sampled weekly for the required measurements. The strains and sexes were reared in separate pens, using 4 replications of 120 birds each. Four feeds, based on corn and soybeans, were used during the trial: feed 1 from 1 to 7 d, feed 2 from 8 to 28 d, feed 3 from 29 to 49 d, and feed 4 from 50 to 56 d of age (all of the birds were given the same feed for each time interval). All of the birds were weighed weekly and the 4 birds sampled from each strain and sex were weighed, fasted for 24 h, reweighed, killed, eviscerated, and dissected. The breast, drums, thighs, and wings were weighed, packed into identified plastic bags, and stored in a freezer to later be thawed and minced. They were then freeze-dried to obtain the water content, after which they were again milled before analyzing for protein, lipid, and ash using AOAC procedures. The Gompertz equation was fitted to the weights of the body parts as well as to the protein weights of the components. Using data from each individual chicken that was sampled, allometric regressions were fitted to the weights of the physical and chemical components, with ln body protein weight being the independent variable and ln component weight being the dependent variable. Although some of the allometric relationships between the various body parts and body protein weight differed statistically between strains and sexes, these differences were of little commercial significance, suggesting that the relative growth rates of the different body components of the genotypes tested in this trial have not been changed substantially by genetic selection.