WE used multiple-labelling immunofluorescence, intracellular dye injection, electrophysiological recording and confocal microscopy to examine the expression of immunoreactivity to protein kinase C (PKC) and protein kinase A (PKA) in sympathetic ganglia of guineapigs. PKCα and PKCγ were widespread in vasoconstrictor and pilomotor neurons. High levels of PKA RIIα and RIIβ were restricted to neurons that lacked significant expression of PKC, including somatostatin-containing neurons projecting to the gut, and non-noradrenergic vasodilator neurons. In coeliac ganglia, most neurons with PKC contained neuropeptide Y and displayed phasic patterns of action potential firing, often with a long after-hyperpolarization. Tonically firing neurons lacked both neuropeptide Y and PKC. These results show remarkably pathway-specific expression of protein kinases in functionally identified populations of sympathetic neurons.