1. I recorded ATP-gated channels from excised outside-out patches from rat sympathetic neurons. The channels had a unitary conductance of approximately 12 pS at -80 mV, were activated only when ATP was present in the bath, and could be blocked by the P2-purinoceptor antagonist suramin. 2. The open probability of the channels showed a strong voltage dependence, increasing significantly with hyperpolarization. This suggests that whole cell rectification of currents evoked by P2X receptor activation is a result of channel voltage dependence and not of properties of ion permeation. 3. Low concentrations of extracellular Zn2+, which has previously been shown to potentiate whole cell ATP-evoked currents, increased the open probability of ATP-gated channels without altering the unitary conductance. 4. Zn2+ increased both the opening frequency and the burst duration of ATP-gated channels. The results are consistent with Zn2+ acting as an allosteric modulator of the P2X receptor in sympathetic neurons.