Retention in the animal body was studied in a growth experiment with lambs of various genetic constructions (3 different fattening hybrids of both sexes and male merino meat sheep). The result of the control butchering method was for female animals a significantly higher crude fat, dry matter and energy content as well as lower crude protein content in the weight gain than for the male animals, whereas there were no significant differences between the various genotypes. The daily crude protein retention was higher in the male animals as in the female lambs. The male fattening hybrids were superior to the merino meat sheep with regard to daily N retention and the productive protein value. Concerning energy maintenance requirement, there were no significant differences between the genotypes or the sexes either. The N balance method resulted in similar statements on N retention as the control butchering method did, it produced, however, higher absolute values and a higher standard deviation. Conclusions for the standardization of the requirement and for the methodology of the experiments are drawn.