Abstract: Serum proteins, thyroid hormones and alkaline phosphatase concentrations were measured in Yankasa sheep experimentally infected with T. congolense. Parasitemia occurred in the T. congolense infected sheep immunomodulated with levamisole two days earlier than the infected group without immunodulation.Packed cell volume decreased significantly(p< 0.05) in the infected groups with and without immunomodulation when compared to the controls from the first week of infection up to the end of the experiment. Serum total protein, albumin, Thyroxine (T4) and Triiodothyronine (T3) decreased significantly (p< 0.05) in the infected sheep with and without immunodulation when compared to the controls. Serum Thyrotopin (TSH) and Alkaline Phosphate (AP) did not alter significantly (p>0.05) in the infected sheep with and without immunomodulation when compared to the controls throughout the period of the experiment. In general, levamisole administration did not appear to alter the infection when compared to the infected group without immunomodulation.