NADPH-diaphorase histochemistry, which identifies neural sites of nitric oxide production, demonstrated intensely stained nerve terminals surrounding the cell bodies of a subpopulation of neurons in rat prevertebral celiac and superior mesenteric sympathetic ganglia but failed to comparably label terminals in paravertebral superior cervical ganglia or perikarya in any sympathetic ganglion. The superior mesenteric ganglia of aged and diabetic rats, in which synaptic dysplasia (neuroaxonal dystrophy) is prominent, failed to show involvement of diaphorase containing nerve terminals.