P2X receptors in the nervous system are involved in both neuronal and glial functions. Pharmacological tools to differentiate the seven P2X subunits are limited, hence localisation studies have examined their distribution. Such studies have provided conflicting data on the localisation of the P2X1 receptor subunit in the CNS. We therefore tested for the presence of the P2X1 subunit in the CNS, using tissue from P2X1 subunit knockout (KO) mice to test the antisera. There was no difference between the CNS of wild type (WT) and KO mice using anti-P2X1 in immunohistochemistry and Western blots. In contrast, the bladder reacted positively only in WT tissue. Thus the P2X1 subunit antibodies cross-react with non-P2X1 receptor proteins in the CNS. Antibody specificity tests should therefore be conducted in the specific tissue to be examined and on KO tissue where available.