A new scheme is presented for identifying 3 sympathetic phenotypes in the rat SCG using electrophysiology and neuropeptide Y expression. Postganglionic compound action potentials recorded from the external and internal carotid nerves each contained two peaks, 1 and 2, with distinct preganglionic stimulus thresholds. Peak 2 in the external carotid response contained subpeaks 2a and 2b having a similar stimulus threshold. Neurons corresponding to peaks 1, 2a and 2b were identified intracellularly by antidromic stimulation, graded preganglionic stimulation, injection with neurobiotin and immunostaining. Seventeen of 53 neurons studied this way had a low threshold for preganglionic stimulation of firing that corresponded to activation of extracellular peak 1. All low threshold neurons were NPY-negative. The other 36 neurons had a high presynaptic stimulus threshold that corresponded to activation of extracellular peak 2, and 12 of these cells contained NPY. Together with other known features of ganglionic organization, the results indicate that low threshold, NPY-negative neurons are secretomotor cells projecting to salivary glands, that high threshold NPY-negative neurons are pilomotor cells responsible for extracellular peak 2a, and that high threshold, NPY-positive neurons are vasoconstrictor cells responsible for peak 2b. Secretomotor, pilomotor and vasomotor neurons identified in this way had distinct axonal conduction velocities (0.52, 0.20 and 0.10 m/s) and diameters (33, 29 and 25 µm), but were indistinguishable in terms of preganglionic conduction velocities (0.30-0.34 m/s) and number of primary dendrites (8.4-8.6). The cell classification scheme presented here will allow future comparison of ganglionic integration in different sympathetic modalities.