The electrophoretic pattern of 130 serum samples from clinically normal dogs was evaluated, using agarose as the supporting matrix. The relative mobility of each globulin fraction in relationship to the mobility of albumin was determined in 70 dogs, and nomenclature based on the mobilities (Rf values) was proposed. Biuret protein determinations were done, and relative and absolute values of each serum protein fraction were determined. Changes in the fractions of serum proteins were evaluated in regard to sex and age of the dogs and the presence of microfilariae of Dirofilaria immitis, as determined by modified Knott tests.