The effect of the suramin analogue 8,8′-(carbonylbis(imino-4,1-phenylenecarbonylimino-4,1-phenylenecarbonylimino))bis(1,3,5-naphthalenetrisulfonic acid) (NF279) was analyzed on human P2X₁ and P2X₇ receptor subtypes (human P2X₁ and human P2X₇) heterologously expressed in Xenopus oocytes using the two-microelectrode voltage-clamp technique. At activating ATP concentrations of 1 μM (human P2X₁) and 10 μM ATP (human P2X₇) , IC₅₀ values of 0.05 μM and 2.8 μM were found for human P2X₁ and human P2X₇ receptors, respectively. An increase in the activating [ATP] shifted the NF279 concentration–inhibition curve rightwards for both receptors. NF279 slowed the activation of both human P2X₁ and human P2X₇ as well as the desensitization of human P2X₁. The data support a model in which desensitization of P2X₁ is dependent on preceding activation of these P2X receptors. It is concluded that NF279 acts as a competitive antagonist with much higher potency at human P2X₁ than at P2X₇ receptors. NF279 may hence be suited to discriminate between both receptors in native tissues.