Most of the specific monoamine fluorescence of the fowl neurohypophysis is found in the eminentia mediana and the infundibular stem. The densest accumulation of fluorescent structures is located to the zona externa and the subependymal layer, whereas generally only scattered fluorescence is demonstrable in the fiber layer. The neural lobe tissue is provided with very fine smooth fibers often difficult to distinguish. Spectrofluorimetric determinations have shown that noradrenaline is the major catecholamine in the chick neurohypophysis. From the embryological studies it is evident that the monoamine fluorescence first appears in the subependymal layer, the fiber layer and the neural lobe (after about 15 days of incubation). The zona externa fluorescence is not visible until just before hatching. 10 days after hatching the fluorescence intensity of the chick neurohypophysis is similar to that of the adult. Some comparisons are also made with the appearance of monoamines in the mouse.