Spinal cord cells from embryonic chicks were cultured upon liver and kidney feeder layers of similar species origin. Successful cultures were obtained with inocula of cord cells containing as few as 15 000 cells ml(-1), whereas without feeder layers at least 200 000 ml(-1) are ordinarily required. Upon liver, many neurons and processes became intensely fluorescent, a property seldom shared by those grown upon kidney. Many processes upon liver contained large numbers of dense-cored vesicles, significantly larger and more numerous than in those grown upon kidney. We conclude that association with liver feeder layers has the consequence of producing in cord cells fluorescence and ultrastructural characteristics appropriate to catecholamine content, through a mechanism as yet unknown.