There has been controversy over the possible lymphoid origin of certain dendritic cell (DC) subtypes. To resolve this issue, DC and plasmacytoid pre-DC isolated from normal mouse tissues were analyzed for transient (mRNA) and permanent (DNA rearrangement) markers of early stages of lymphoid development. About 27% of the DNA of CD8+ DC from thymus, and 22–35% of the DNA of plasmacytoid pre-DC from spleen and thymus, was found to contain IgH gene DJ rearrangements, compared with 40% for T cells. However, the DC DNA did not contain IgH gene VDJ rearrangements nor T cell Ag receptor β gene DJ rearrangements. The same DC lineage populations containing IgH DJ rearrangements expressed mRNA for CD3 chains, and for pre-Tα. In contrast, little of the DNA of the conventional DC derived from spleen, lymph nodes, or skin, whether CD8+ or CD8−, contained IgH DJ rearrangements and splenic conventional DC expressed very little CD3ε or pre-Tα mRNA. Therefore, many plasmacytoid pre-DC and thymic CD8+ DC have shared early steps of development with the lymphoid lineages, and differ in origin from conventional peripheral DC.