To study the influence of rbST on puberty incidence of Friesian heifers in relation to progesterone (P4), growth hormone (GH), insulin like growth factor (IGF-I), glucose and urea-N in blood plasma, total of 16 Friesian heifers having 187.63±2.56 kg live body weight and 8.23±0.59 months of age were divided into two similar groups, 8 animals each. Animals in the first group (G1) were subcutaneously (s.c.) injected with saline (0.9% Nacl) while, animals in the second group (G2) were s.c. injected with 250 mg rbST 14 d-interval for five times pre-puberty. Feeding system and management were the same for both groups. Blood samples were collected to determine concentration of P4, GH, IGF-I, glucose and urea-N in blood plasma throughout the experimental period from 8.2 mo of age up to puberty. Results show insignificant differences in average P4 concentration during 3 wk pre-puberty, P4 peak pre-puberty and interval from P4 peak to puberty. The interval from 1^st rbST injection to puberty was earlier (83.67 vs. 136.0 d, P<0.05) and LBW was lighter (254.6 vs. 279.1 kg) in G2 than in G1. Concentration of P4 at puberty was not affected by treatment. Average age at puberty was 342 and 391d in G2 and G1, respectively. Overall concentration of P4 during the experimental period was nearly similar in G1 and G2, being 0.460 and 0.472 ng/ml, respectively. Concentration of IGF-I and GH was higher (P<0.05) in G2 than in G1 as overall mean or pre- and at puberty. This increase was about 20 and 19% for IGF-I and 61 and 41% for GH pre- and at puberty, respectively. The differences in IGF-I and GH between pre- and at puberty for each group were not significant. Average concentration of IGF-I showed sharp increase post the 1^st rbST injection by about 24.5%. Overall concentration of glucose during the experimental period increased (P<0.05) in rbST group (85.9 mg/dl) as compared to the control group (79.1 mg/dl), although glucose concentration pre- and at puberty was not affected significantly by rbST treatment. Concentration of urea-N was lower (P<0.001) in G2 than in G1 as overall mean (27.5 vs. 32.2 mg/dl). Also, concentration of urea-N reduced (P<0.05) in G2 compared with G1 pre- and at puberty by 15 and 19%, respectively. Pre-pubertal urea-N concentration in heifers showed marked reduction by increasing number of injections, in particular post-1^st injection. The strongest positive correlation was between concentration of GH and IGF-I (r= 0.695, P<0.001). In conclusion, rbST treatment at a level of 250 mg at 14- day interval for five times pre-puberty is strongly in relation to concentration of GH and IGF-I and in less extend to glucose and urea-N concentration to induce precocious puberty in Friesian heifers.