This study focused on whether bone marrow would differentiate tolerogenic dendritic cells (DCs) by comparing interleukin-3 (IL-3) DCs (induced by IL-3+IL-4) with GM-CSF DCs (induced by GM-CSF+IL-4, generating myeloid DCs). Mouse bone marrow progenitors were induced in vitro to differentiate into DCs by exposure to IL-3. The morphology and yields of IL-3 DCs and GM-CSF DCs were compared by scanning electron microscopy and laser scanning confocal microscopy. Immunohistochemistry and flow cytometer (FCM) were used to identify immune phenotypes. The results showed that IL-3 DCs and GM-CSF DCs both expressed the specific marker DEC-205 with about 80% and 70% purity, respectively. IL-3 DCs had similar morphology as plasma cells, but a different immune phenotype, namely, CD80(-), CD86(-), CD14(-), and MHC class II(+). IL-3 DCs remained in the costimulatory molecule-deficient state when TNF-alpha was supplemented into the culture. We therefore propose that IL-3 induces a high purity and yield of DCs from bone marrow. Since IL-3 DCs possess a tolerogenic phenotype (MHC class II(+), B7(-)), they may induce alloantigen-specific hyporesponsiveness in vitro.