It has been established that embryogenesis is accompanied by the intense production of nitric oxide (NO). Based on available data, the rate of NO production is roughly equal in all embryos of the same poultry species. However, the rate of NO oxidation to nitrate in embryos of meat breeds is higher than in embryos of egg breeds. In broiler embryos about 90% of all produced NO is oxidised to nitrate. In embryos from egg breeds only several per cent of the NO oxidised to nitrate and the other NO is stored in the embryonic tissues included in NO donors. The intensity of NO oxidation in bird embryo is not depended on sex, age of the layer and feeding regime. Intensity of oxidation varies by no more than 10% within a breed strain or cross. Breeding to increase meat productivity is always associated with an increase in the intensity of NO oxidation in the embryo. There is no direct relationship between the increase in NO oxidation and the live weight gain. It can vary from hundreds of percent to several percent depending on the breed. Moreover, morphological differences between breeds with high and low intensity of embryonic NO oxidation are manifested only after hatching, as synthesis of NO is much lower than in the embryo. It has been presumed that NO oxidation is associated with the synthesis or activation of the factor(s) involved with enhanced growth of meat tissue. This is predetermined genetically and can be partly induced by exogenous stimulants, such as green light. The rate of embryonic NO oxidation can therefore be a useful criterion in practical selection of poultry and in the evaluation of growth enhancers acting at the embryonic level.