The vasculature of the arteriole-glomerular units in variou« zones of the rat kidney was studied by micro-angiography, and the adrenergic innervation of these units by the histochemical fluorescence method for biogenic monoamines. In the cortical unit the afferent arteriole, glomerular tuft and efferent arteriole are coupled in series, whereas in the juxtamedullary unit the glomerular capillaries bud off as lateral twigs from a continuous arteriole which leads into the medulla. These findings of an extraglomerular medullary circulation have previously been demonstrated in man and rabbit. The cortical and juxtamedullary units have similar innervation patterns with adrenergic nerve terminals along both the afferent and efferent arterioles. These findings agree with evidences presented by others of neurogenic contractions of both pre- and postglomerular vessels. The adrenergic innervation of the continuous juxtamedullary arterioles constitutes a morphological basis for neurogenic variations in the magnitude of the extraglomerular circulation in the kidney with consequent changes of GFR and FF.