The central respiratory-drive-related inputs to antidromically identified cervical sympathetic preganglionic neurones have been investigated, in the rat, using extracellular recording techniques, the ionophoretic application of an excitatory amino acid (glutamate) to increase their excitability, and phrenic nerve discharge as an indicator of central respiratory drive. Three distinct firing patterns of sympathetic preganglionic neurones are described: maximal discharge during phrenic nerve activity, maximal discharge during phrenic silence, and a firing pattern unrelated to phrenic nerve discharge. Both spontaneously active and glutamate-activated silent cervical sympathetic preganglionic neurones had similar, if not identical, firing patterns. The application of glutamate, using ionophoretic currents of up to 100 nA, did not disrupt central respiratory-drive-related discharge patterns indicating that these inputs are an important contribution in the regulation of the firing pattern of a proportion of sympathetic preganglionic neurones. On the basis of these observations it is proposed that some sympathetic preganglionic neurones may receive central respiratory drive potentials similar to those received by respiratory motoneurones.