An indirect hemagglutination test was developed for detecting antibody against Bovine Leukemia Virus. Medium from Bovine Leukemia Virus infected monolayer fetal lamb kidney cell line cultures was concentrated by a combination of ammonium sulfate precipitation and freezedrying. Tanned sheep red blood cells were exposed to p24 and GP antigens, separately and together. The GP antigen did not attach to the sheep red blood cells, while the p24 antigen did. On testing 150 samples from suspect animals with the crude antigen-coated sheep red blood cells, the indirect hemagglutination test detected almost the same number (74) of positive animals as the agar gel immunodiffusion test with GP antigen (79), and by each of these test a far greater number of cases of leukosis were detected than by hematologic examination (58) or agar gel immunodiffusion test with p24 antigen (44). These results suggest that the indirect hemagglutination test may detect almost the same number of positive as the agar gel immunodiffusion test with GP antigen. Moreover, its results can be read two days earlier, and an impression of the antibody level in the sera is obtained. In routine or large-scale work the indirect hemagglutination test is too troublesome and time-consuming compared to the agar gel immunodiffusion test. The indirect hemagglutination test may be improved if it becomes possible to sensitize sheep red blood cells with GP antigen.