Dendritic cells (DC) have an increasingly important role in vaccination therapy; therefore, this study sought to determine the migratory capacity and immunogenic function of murine bone-marrow (BM)-derived DC following subcutaneous (s.c.) and intravenous (i.v.) injection in vivo. DC were enriched from BM cultures using metrizamide. Following centrifugation, the low-buoyant density cells, referred to throughout as DC, were CD11c(high), Iab(high), B7-1(high) and B7-2(high) and potently activated alloreactive T cells in mixed lymphocyte reactions (MLR). In contrast, the high-density cells expressed low levels of the above markers, comprised mostly of granulocytes based on GR1 expression, and were poor stimulators in MLR. Following s.c. injection of fluorescently labelled cells into syngeneic recipient mice, DC but not granulocytes migrated to the T-dependent areas of draining lymph nodes (LN). DC numbers in LN were quantified by flow-cytometric analysis, on 1, 2, 3, 5 and 7 days following DC transfer. Peak numbers of around 90 DC per draining LN were found at 2 days. There was very little migration of DC to non-draining LN, thymus or spleen at any of the time-points studied. In contrast, following i.v. injection, DC accumulated mainly in the spleen, liver and lungs of recipient mice but were largely absent from peripheral LN and thymus. The ability of DC to induce T-cell-mediated immune responses was examined using trinitrobenzenesulphate (TNBS)-derivatized DC (TNBS-DC) to sensitize for contact hypersensitivity responses (CHS) in naive syngeneic recipients. Following s.c. injection, as few as 105 TNBS-DC, but not TNBS-granulocytes, sensitized for CHS responses. However, the same number of TNBS-DC failed to induce CHS following i.v. injection. In summary, this study provides new and quantitative data on the organ specific migration of murine BM-derived DC following s.c. and i.v. injection. The demonstration that the route of DC administration determines the potency of CHS induction, strongly suggests that the route of immunization should be considered in the design of vaccine protocols using DC.