The CB1 receptor and the splice variant CB1a are localized mainly in the brain.{6628,6726,6724} The CB1 receptor is a G-protein coupled receptor that binds the active component of cannabis, ?9-tetrahydrocannabinol. Human and rat CB1 receptors exhibit 97.3% homology at the amino acid level over the complete protein, and 100% homology within the peptide sequence used to make this antibody.{6629,6628} This peptide exhibits no homology with the CB2 receptor. Based on the amino acid sequence, the CB1 receptor has a molecular weight of approximately 52,800.{6628} The CB1 receptor and the splice variant CB1a are localized mainly in the brain, whereas the CB2 receptor is localized predominantly in peripheral tissues, including the spleen and hemopoietic cells.{6629,6628,6726,6724} Cayman’s CB1 Receptor Polyclonal Antibody can be used for Western blot and immunohistochemistry applications. The antibody recognizes the N-terminal extracellular region of the CB1 receptor at 40 kDa from human samples.