A complete diallel cross of four broiler breeds was made to investigate whether there are breed differences in the combining abilities for the traits, body weight, weight gain and feed efficiency, measured during the growing period from 4 to 12 weeks of age. Data collected from male and female birds were analysed separately. General combining ability (GCA) was found to be the largest and most significant source of variation contributing to differences between crosses for all the traits, in both male and female birds. Specific combining ability (SCA) was important for body weight in both sexes and for weight gain in females. Feed efficiency in both sexes did not appear to be influenced by SCA effects. Reciprocal effects (RE) were generally absent in both sexes for all the traits, except possibly for feed efficiency.