The suramin analogue 8,8′-(carbonylbis(imino-4,1-phenylenecarbonylimino-4,1-phenylenecarbonylimino))bis(1,3,5-naphthalenetrisulfonic acid) (NF279) was analysed with respect to its potency and P2X receptor subtype selectivity. Two-electrode voltage-clamp measurements were performed with Xenopus laevis oocytes expressing homomultimeric rat P2X₁, P2X₂, P2X₃ and human P2X₄ receptors. For the fast desensitising P2X₁ and P2X₃ receptors, IC₅₀ values strongly depended on whether oocytes were pre-incubated with NF279 prior to ATP superfusion or exposed to NF279 simultaneously with ATP. With a 10 s pre-incubation period of NF279, IC₅₀ values of 19 nM and 1.62 μM were obtained for rat P2X₁ and P2X₃, respectively. Without pre-incubation, IC₅₀ values amounted to 2 μM and 85.5 μM for P2X₁ and P2X₃, respectively. For the non-desensitising rat P2X₂ receptor NF279 appeared to act as a competitive antagonist with an IC₅₀ value of 0.76 μM and a K_B value of 0.36 μM, as derived from Schild analysis. P2X₄ receptors were the least sensitive subtypes for NF279 (IC₅₀>300 μM). The antagonism was fully reversible at all P2X subtypes analysed. Our results indicate that NF279 is a potent P2X₁ receptor-selective and reversible antagonist.