Parabiosis experiments demonstrating that dendritic cells (DCs) do not equilibrate between mice even after prolonged joining by parabiosis have suggested that DCs are derived from self-renewing progenitors that divide in situ. However, here we found that unequal exchange of DCs between mice joined by parabiosis reflected uneven distribution of DC precursors in blood due to their short half-life in circulation. DCs underwent only a limited number of divisions in the spleen or lymph nodes over a 10- to 14-day period and were replenished from blood-borne precursors at a rate of nearly 4,300 cells per hour. Daughter DCs presented antigens captured by their progenitors, suggesting that DC division in peripheral lymphoid organs can prolong the duration of antigen presentation in vivo.