2.5% Normal Horse Serum is used for blocking non-specific binding when horse secondary antibodies are used in immunohistochemistry assays. This ready-to-use solution is the same serum preparation that is included in the ImmPRESS Detection Systems and R.T.U. VECTASTAIN ABC Kits, and can also be used as an antibody diluent. Vector produces this serum by collecting and pooling the sera from healthy adult horses, heat-treating and centrifuging the pool to remove precipitates, and then filtering to remove fine particulates. The serum is tested with antibodies to check for possible cross-reactivities and then diluted to 2.5% (v/v) in buffer containing 0.08% sodium azide.