This study was carried out to determine the origin of the meat used in heat processed sausages. For this purpose, sausages prepared from pure beef and horse meat and sausages prepared with different mixture rates of these meats, were cooked in a smoking oven at 75 degrees C for 15 minutes. Proteins of extracts from these heat-processed sausages were separated by the isoelectric focusing technique. Only myoglobin bands of these gels prepared by this technique, were stained by the pseudoperoxidase staining method. Species differentiation was easily performed with sausages made from pure beef and horsemeat. Similarly determination of these two species in mixed sausages containing high rates of horse meat was possible by observation of bands from beef and horsemeat together. However, determining the horsemeat was not possible with sausages in which the horse meat rate in beef was 20% or below.