ARL 67156 trisodium salt is a newly synthesized analog of ATP which functions as a selective ecto-ATPase inhibitor. In addition, studies suggest that ARL 67156 also acts as a weak antagonist for the purinoceptors P2X and P2T and as an agonist for P2u. A common problem observed in the pharamacological classification of receptors is the susceptibility of antagonists and agonists to enzymatic degradation by the assay tissue used, which ARL 67156 may possibly resolve. It has been reported that ARL 67156 also potentiates the effects of UTP, ATP-γ-s, and ATP on purinoceptors via inhibiting dephosphorylation. Furthermore, this ATP analogue can be used as a probe to determine the action of nucleotides and in the classification of purinoceptors.