In this study, 14 Holstein heifers were used. Animals were divided into two groups. Ftekombinant bovine somatotropin (rBST) was injekted 14 mg/day daily one of the groups during 196 days. The effects of rBST on milk yield, milk composition, feed intake, some postpartal reproductive parameters, blood glukoz, insuline and non es-terifed fatty acids levels were investigated. During ten weeks at the pretreatment, milk yield was measured and these values were used in covarians analysis. Milk yield was significantly increased by the rBST treatment. Before the rBST administration average milk yield of control and treatment group were 15.33 kg and 14.04 kg respectively. These datas were became equal in the first month of the experiment and were observed as 13,76 kg for the control group, 13.52 kg for the treatment group. Then milk yield was more at the rBST administred group than the control group during the last months of the experiment. Concentrate feed was gi ven to animals relative to their milk yield and chopped alfalfa hay was given ad libitum. There were no differences between groups for the alfaifa hay intake. No negative effects of rBST treatment were observed on early pospartum sign and ovarial functions. Milk composition, blood in* silune, glucose and non esterified fatty acids levels were not affected by the hormone administration.