Acetylcholine (ACh) and adenosine-5'-triphosphate (ATP) are candidate neuromodulators which regulate the excitability of spiral ganglion neurons (SGNs) at the efferent lateral terminals below inner hair cells. Using the whole-cell patch clamp recording technique, the present study characterizes the ionic conductances activated by ACh and ATP in isolated SGNs. Brief application (1s) of ACh evoked in a dose-dependent manner (EC₅₀ = 4.1 µM) a reversible inward current when SGNs were voltage-clamped at -50 mV. The cholinergic current developed with a long latency (average 1.3 s), was reversibly blocked by atropine and mimicked by muscarine. These results suggest the involvement of muscarinic receptors. Application of ATP also evoked a reversible inward current at Vh=-50 mV, but the current showed two components. A fast component with a short latency was largely reduced when N-methy-D-glucamine (NMDG) replaced extracellular sodium. This current was presumably due to a P2X-like ionotropic conductance. The second component had a longer latency (average 1.1s) and was presumably activated by metabotropic P2Y-like receptors. The second component of ATP-evoked current shared similar characteristics with the responses evoked by ACh: the current reversed near 0 mV, displayed inward rectification, could be carried by NMDG, and was insensitive to extracellular and intracellular calcium. This non-selective cation conductance activated by ATP or ACh was reversibly inhibited by a pre-application of ionomycin. These results suggest that ACh muscarinic receptors and ATP purinergic metabotropic receptors activate a similar large non-selective cation conductance via a common intracellular biochemical pathway in SGNs. This depolarizing response evoked by ATP and ACh is a candidate mechanism to regulate neuronal excitability of cochlear SGNs.