Bovine leukemia virus (BLV) has a long latency period during which animals are inapparently infected, may spread the disease, and are only detected by serological techniques or by the most cumbersome molecular biology techniques. We have compared techniques for detecting either total antibodies (ELISA), anti-p24 and Gag-related proteins (Western blot), or anti-gp51 (agar gel immunodiffusion, AGID, and syncytia inhibition, SI) in rabbits inoculated experimentally with inocula of variable immunogenicity. The two tests to detect antibodies to gp51 correlated well in sera clearly positive or clearly negative by either one, but correlation was poor in the intermediate groups. All sera positive by AGID were also positive by ELISA, but results did not agree in sera negative by AGID, ELISA proving to be more sensitive. Western blot was a good technique for detecting antibodies against Gag-related proteins. However, no band was identified to clearly correspond to anti-Env-related proteins. As for other retroviruses, testing of animals for infection with BLV should include the detection of antibodies anti-Gag and anti-Env proteins.