Zeranol (resorcylic acid lactone, Ralgro) is one of the most widely-used growth agents in beef catties and lambs in our country. Forty-five male lambs of Konya Merino were used in trial. The effects of Zeranol on haematological values and some blood metabolites were investigated. This study was made as three groups. There were fifteen male lambs in each group. Group I (Control), Group II and Group III were respectively, control (no implanted), 112 mg Zeranol implanted and twice 12 mig Zeranol implanited at forty days intervals. This trial was continued on ninety days. Blood samples were taken at fifteen days intervals.

Implantation had no significant effect on haematological values of lambs. It was determined that the limits of variation of red blood cell (RBC) count of Group I, Group II and Group III were respectively; 785. - 10.31 x10⁶ 6.86-10.02 x10⁶ and 8.15 -10.80 x10⁶/mm³. Group III had lower white blood cell (WB'C) count than Group I and Group II up to sixtyth days, but after that they had higher than other groups. Implanted lambs had lower mean haemoglobin (Hb) concentration than control lambs. The sedimantation rate of stored blood (ESR) was generally found the similar pattern among groups.

The ammonia nitrogen value; from blood metabolites which had been analysed were higher in implanted than in control lambs but the serum urea nitrogen values were generally lower. The serum total protein values were approximetaly same in all groups.