Doxepin (DOX) and imipramine (IM) administered by close intra-arterial injection (25, 40 and 60 μg/kg) potentiated the inhibitory effect of norepinephrine (NE) on electrically-evoked postganglionic potentials in the superior cervical ganglion of the cat. Dose-response relationships indicated no significant difference between DOX and IM with regard to their effect on NE activity. Potentiation of dopamine (DA)-induced suppression of ganglionic transmission by DOX and IM (25, 40 and 60 μg/kg) was not as pronounced as the potentiation of NE activity by these two antidepressants. Significant potentiation of DA was evident only at the 40 and 60 μg/kg dose levels of DOX and IM. Dose-response relationships indicated that potentiation of DA by DOX was significantly greater than that produced by IM. © 1975.