Some methods were studied comparatively with 45 serum samples collected from diseased race horses for diagnostic purposes and 38 from healthy race horses. All the samples gave positive cephalin-cholesterollecithin flocculation tests at a medium degree or higher, and negative thymol turbidity tests and negative Hayem tests, without exception. Accordingly, these three tests were not applicable to race horses at all. It was difficult and required skill to read the endpoint of the Gros test in any one of the samples. Ucko's modification of the Takata test and the sublimate test, both of which showed an intimate relationship with the albumin-globulin ratio, were proved to be of high value when applied to race horses. The Lugol test with its simple technique was the most fitted one for screening to clarify an increase in globulin content. The zinc sulfate turbidity test was found to be of high clinical value, since it was closely related to a rise and fall of gamma-globulin content in race horses.