Lymph-borne dendritic cells (L-DC) collected from the thoracic duct of rats following mesenteric lymphadenectomy are derived from the small intestine. We have cultured these cells in vitro and examined their survival and phenotypic and functional changes. L-DC survive poorly in culture in normal media (less than 50% overnight) but survival can be markedly increased by supplementation with Con A-stimulated spleen cell supernatant or recombinant granulocyte-macrophage colony-stimulating factor (GM-CSF) but not by recombinant IL-1, IL-2, IFN-gamma or by an IL-3-rich supernatant. The effects of GM-CSF are blocked by a specific antiserum. L-DC display heterogeneity for some surface markers, cytoplasmic inclusions and enzyme reactivity. After 16-48 hr culture the pattern of expression is markedly different. The numbers of Thy-1-positive L-DC and the amount of Thy-1 expressed increases, as do the numbers of L-DC expressing OX48 antigen. All L-DC remain Ia positive, but the proportion expressing the iC'3b receptor, non-specific esterase or cytoplasmic DNA inclusions decreases to almost zero. In contrast to Langerhans' cells, fresh L-DC are potent stimulators of an allogeneic mixed leucocyte reaction (MLR) but their potency is considerably increased after 16 hr culture. Also in contrast to Langerhans' cells, the increase in potency is not affected by culture with CAS and is thus unlikely to be dependent on GM-CSF. The changes described in L-DC properties could be related to their role as antigen-presenting cells.