We have determined whether particular lymphocyte populations bind preferentially to cerebral endothelium, using adhesion assays and a new method for in situ staining of adherent lymphocytes. B cells bind more strongly than T cells, an effect enhanced by lymphocyte activation or endothelial cell stimulation with interferon-gamma (IFN-gamma) or tumour necrosis factor-alpha (TNF-alpha). This is not equated with levels of CD18 expression on the lymphocytes. CD8+ T cells bound more efficiently than CD4+ cells under all conditions. To determine whether there was a population of cells which selectively homes to the brain, we compared adhesion of cervical lymph nodes cells to brain endothelium, with adhesion of lymphocytes from other nodes. In 50% of the experiments there was significantly enhanced binding of activated cervical lymph cells to cerebral endothelium but not to control (aortic) endothelium. This effect was seen using both normal and IFN-gamma-activated endothelium. The explanation for this finding is that cervical lymph nodes frequently, but not invariably, contain higher proportions of CD8+ cells and B cells than other lymph nodes. These data imply that selective adhesion of lymphocytes to brain endothelium is related to the subpopulations involved and this may be reflected in the cell types seen in immunological lesions of the brain, and in the relative proportions of the subpopulations seen in cervical lymph nodes.