The IDEXX Leukosis Blocking Ab Test detects specific antibodies directed to the BLV gp51 antigen in both individual sera and pools of 10 sera. It is based on the competition between the BLV antibodies of the bovine serum and a peroxidase conjugate monoclonal anti-gp51 BLV antibody. It is an important complement to the indirect BLV ELISA that uses an ultrapurified BLV lysate. It is standardized to detect the European standard for serum (E5) diluted to 1:100 in negative bovine serum, according to the requirements of the Council Directive 64/432/EEC (modified on the December 11, 1984, June 26, 1991 and March 2001).