1. Extraneuronal uptake of noradrenaline (NA) was examined in the cat spleen first by perfusing with NA for 10 min, followed by a 2-min wash to clear the extracellular fluid, then measuring the amount retained, its subcellular distribution and the tissue components involved as revealed by the development of the characteristic fluorescence. Secondly, thin spleen slices were exposed to NA in vitro and the development of fluorescence in various structures, particularly arterial smooth muscle, measured.2. The cat spleen accumulated large quantities of NA and this, like the development of fluorescence, was concentration-dependent. After particle separation most of the retained amine appeared in the high-speed supernatant, with a lesser amount in the coarse granule fraction. There was little amine in either the mitochondrial or microsomal fraction. The microsomal fraction from unperfused spleens was rich in NA, presumably from storage granules from the adrenergic nerves. On an intermittent sucrose density gradient the NA-rich particles sedimented between 1.0 and 1.5 M sucrose, corresponding to the recently described dense granules from bovine splenic nerves.3. Fluorescence histochemistry revealed several tissues accumulating NA. At an NA concentration of 10(-5) g/ml., arterial smooth muscle and endothelium showed intracellular fluorescence; at 10(-4) g/ml., collagen, the perimeter of the smooth muscle cells of the capsule-trabecula-vein system and the reticular cells forming the framework of the spleen developed fluorescence. In the reticular cells the fluorescence was intracellular. The fluorescence pattern on the perimeter of non-arterial smooth muscle corresponded to the pattern of basement membrane as shown by PAS staining. The red pulp, lymphoid tissue and the phagocytic cells of the ellipsoids did not fluoresce.4. Cooling the tissue to 15 degrees C or less, phenoxybenzamine in a concentration of 5 x 10(-5) g/ml. or normetanephrine in a concentration of 10(-4) g/ml. prevented both uptake and loss of NA in arterial smooth muscle but had no effect on collagen.5. Chronic post-ganglionic denervation or reserpine had no effect on the development of fluorescence in any extraneuronal tissue.