The objectives of this experiment were to determine serum concentrations of Triiodothyronine (T₃), Thyroxine (T₄), and Thyroid Stimulating Hormone (TSH) following administration of the anthelmintic Doramectin in healthy donkeys. This was done to investigate the sub acute effect of doramectin injectable formulation in donkeys. Serum T₃, T₄ and TSH concentrations in serum samples obtained before and after doramectin administration for continuous        7 days, were determined using RIA technique. Baseline values ranged from 0.32 to 1.63 ng of T₃/ ml, 3.13 to 22.61 ng of T₄/ ml, and           0.34 – 1.01 mIU/L of TSH. There are no significant (P>0.05) differences between the treatment groups and the control for the concentration of the three hormones under investigation, but there is significant increase in the level of hormones when compared with the pre treatment level in all groups.