Fluorescence-histochemical investigations by use of the FAGLU method show the presence of several groups of catecholamine (CA)-containing neurons in the chicken brain. The distribution, shape and orientation of the fluorescent perikarya as well as the number and orientation of primary dendrites have been systematically examined. In the chick embryo, the first neurons displaying specific catecholamine fluorescence are identifiable on the 9th day of incubation. The onset of this type of specific fluorescence is consistent with biochemical data reported in the literature for the chick embryo. The main complexes of CA-containing cell bodies, shown at medullary, pontine and mesencephalic levels, display a pattern of distribution that is quite similar in both the chicken and the rat. In the hypothalamus of chick embryos and newly hatched chicks. CA-containing neurons have been localized within the paraventricular organ, and the periventricular and mammillary regions. By the fourth week after hatching, within the hypothalamus the paraventricular organ alone continues to display fluorescent neurons.