NS383 is a potent and uniquely selective inhibitor of rat ASICs containing 1a and/or 3 subunits. NS383 inhibits H(+)-activated currents recorded from rat homomeric ASIC1a, ASIC3, and heteromeric ASIC1a+3 with IC50 values ranging from 0.61 to 2.2 μM. NS383 is well tolerated and capable of reversing pathological painlike behaviors, presumably via peripheral actions, but possibly also via actions within central pain circuits.