Development and maturation of the catecholamine-containing neurons of the embryonic chick and quail Remak's ganglion were studied, using the glyoxylic acid method. Fluorescent neurons were detected in the pararectal segment of the ganglion from its earliest in vivo formation, and along the whole ganglionic chain in later developmental stages. In tissue culture, a large number of catecholamine-containing neurons matured in explants of both early and more developed ganglia, producing an extensive network of outgrowing fluorescent nerve processes. Pararectal ganglia, cultured in vitro for up to 4 days, gave rise, whatever the developmental stage examined, to fluorescent migratory neurons distributed either in ganglion-like clusters or singly in a large area surrounding the explant. Many non-fluorescent neurons were intermingled with the fluorescent ones in the explants, as well as in the outgrowth. Ganglia from segments adjacent to the small intestine did not give rise to migratory neurons whatever the developmental stage. Regional differences in the development of migratory neurons may be correlated to the mechanism of the in vivo organization of the ganglionic chain. The present observations indicate that catecholamine-containing neurons in Remak's ganglion exhibit the same histochemical features as adrenergic sympathetic neurons and differentiate in short-term cultures.