Potential changes in the activity of endocrine axes related to growth as a result of leptin administration during embryonic development of birds were evaluated in the Japanese quail as a model bird with fast growth and development. On day 5 of incubation, 0.1 µg or 1 µg of recombinant mice leptin in 50 µl of phosphate buffered saline were injected into the albumen of eggs. Animals from each group were killed by decapitation on day 0, 2, 5, 7, 14, 21, 28, 35, 42, 49 and 56 of life. Plasma concentrations of triiodothyronine (T3), thyroxin (T4), corticosterone, testosterone, total lipids, triacylglycerols, cholesterol, glucose and alkaline phosphatase activity were measured. Quail treated by leptin hatched earlier (5-24 hours) and had a higher body weight than the control group (P<0.05-0.001). Mean body weight across the whole observed period was higher in both treated groups as compared to the control group (P<0.05). Leptin in ovo administration was accompanied by changes of endocrine and metabolic parameters during postembryonic development. The most prominent changes appeared immediately after hatching (T3, T4, total lipids, triacylglycerols) and before sexual maturity. It is suggested that leptin acts as a general signal of low energy status to neuroendocrine systems in birds which improves utilization of nutrients., D. Lamošová, M. Máčajová, M. Zeman, Š. Mózeš, D. Ježová., and Obsahuje bibliografii