The neural crest is a transient embryonic structure that originates from the dorsal surface of the neural tube. Soon after their appearance, the crest cells migrate throughout the body and differentiate into a variety of cell types8, 25, 26. We have recently discovered z4 that in rat embryo the enzymes tyrosine hydroxylase (TH) and dopamine-fl-hydroxylase (DBH), which specifically subserve the synthesis of norepinephrine, could be detected with immunohistochemical techniques when the crest cells reached the region of the future sympathetic chain. Some of these cells formed the sympathetic chain, while others, also containing TH and DBH, migrated alongside the aorta to form the paraganglia and adrenal medulla. In the course of this study we also detected the presence of cells containing TH in the embryonic gut wall. Since the gut of adult rats lacks intrinsic noradrenergic neurons 3, several questions were raised: first, whether the cells containing TH disappear prior to or after birth, and second, whether these cells contained not only TH but also DBH and phenylethanolamine-N-methyltransferase (PNMT) and hence, if they could be defined as dopaminergic, noradrenergic or adrenergic. Pregnant albino rats (Sprague-Dawley) were purchased from a commercial animal colony. The first day of pregnancy was defined as the day the vaginal plug was detected. At the appropriate day of development, pregnant rats were anesthetized with pentobarbitol (40 mg/kg, ip), embryos removed individually from the uterus, fixed by immersion in formalin (4~ paraformaldehyde in 0.1 M phosphate buffer, pH 7.4) for 2 h and embedded in 30~ sucrose at 5 C overnight. The following day the embryos were mounted in 30~ sucrose, frozen with dry ice and 15# m sections cut in a cryostat microtome at--20~ 5 C. The sections were melted onto glass slides. The bound antibody was localized by the peroxidase-antiperoxidase unlabelled antibody enzyme method (PAP technique) of Sternberger z3, as described by Pickel et al. is. The procedure for preparation of the antibodies to TH, DBH and PNMT, as well as the criteria used to judge their specificity, have been previously described 9, 1o, 21.