The aim of this paper is to determine the concentration of blood metabolic hormones and leptin levels in growing lambs. The research was carried out on Tsigai lambs in two periods (suckling and fattening) during the winter feeding season. Lambs were suckling and ate a food mixture and alfalfa hay ad libitum, while during the fattening period they were fed only with the above mentioned mixture and alfalfa hay ad libitum. Their blood was analyzed on 35th and 75th day of age. Concentrations of minsulin, leptin and thyroid hormones were determined in the blood serum of lambs during both periods. In the blood of fattening lambs significantly higher (P<0.01) leptin concentrations (4.83 and 3.45 ng/mL) and slightly higher(P>0.05) insulin concentrations (1.05 and 0.54 μU/mL), were determined, compared to suckling lambs. A significant strong positive correlation between serum leptin and insulin (r = 0.85, P<0.01) was also determined in the blood of fattening lambs and a positive correlation of above mentioned indicators in the blood of suckling lambs, but with no significant difference (r = 0.25, P>0.05). The concentration of thyroid hormones did not significantly differ depending on the period of measurement. These changes indicate that the measurement concentrations of metabolic hormones and leptin in blood are very important in order to understand the changes of metabolism and nutrient supply in growing lambs.