Splenic noradrenergic innervation in young adult and aged Fischer 344 rats was examined using fluorescence histochemistry for catecholamines and high performance liquid chromatography with electrochemical detection (LCEC) for the quantitation of norepinephrine (NE). In young adult rats, abundant noradrenergic plexuses followed the vasculature and trabeculae into splenic white pulp. In aged rats, noradrenergic innervation was reduced in density and in overall intensity of fluorescence, and splenic NE levels were significantly lower. The relationship between diminished noradrenergic innervation and diminished immune responsiveness in aging mammals, while not clear on a causal level, is presented as a hypothesis for further testing.