Three cross breed dogs; referred to the small animal hospital of Tehran university. The most important complaints were the anorexia and sever emaciation. Corneal opacity was obvious in two of these cases. Animals were pyretic (T 40-41°C) and other vital signs were normal. Blood samples collected from the cephalic veins of the dogs, using ethylene diamine tetra acetic acid (EDTA) as anticoagulant (1 mg/ ml). Complete blood cell count showed a non regenerative anemia with low PCV, Hb, RBC, MCV, MCH and MCHC. Thin smears were made and stained by Gimsa method after fixation in methanol and then examined under a light microscope (100 X). Trypanosoma evansi detected with 17-36 µ length (mean 25 µ). The kinetoplasts of the parasites were subterminal, the undulating membranes were well developed and there was a substantial free flagellum. Serum analysis showed hyperproteinemia and normal values of Alanin Aminotransferase, Aspartate Amino transferase and total billirubin. Serum analysis showed a polyclonal gammapathy and a beta-gamma bridge in the electrophoresis of serum samples of two dogs. The gamma fraction in one of these dogs composed 36% and in another case 60% of the whole serum proteins. In these two dogs the amount of increase in gamma2 region which is mainly the region of IgG migration, was much more than Gamma1, it can be resulted that these dogs suffered from a chronic but active antigenic stimulation of infection by Trypanosoma evansi. Decrease in beta globulins was occurred in all of the serum samples. Hypoalbuminemia occurred in two cases as the result of extravasation of albumin due to increased vascular permeability in trypanosomiasi. After confirming the disease, treatment started by Diminazene Aceturate (Brenil, Intervet).