The effects of polar glycopeptidolipids of Mycobacterium chelonae (pGPL-Mc) on haematopoietic stem cells and on megakaryocyte progenitors in bone marrow (BM) and spleen were investigated in mice. We studied the in vivo spleen colony-forming ability and marrow repopulating ability of pGPL-Mc by assays of colony-forming units-spleen (CFU-S). The number of CFU-S was increased in BM when both donors and recipients were treated with pGPL-Mc. In contrast, a single treatment of donors induced enhancement of spleen CFU-S. The number of pre-CFU-S was not significantly increased by pGPL-Mc injection. Megakaryocyte (Meg) progenitors were determined in vitro with a quantitative cultural analysis of bone marrow and spleen cells in agar in the presence of spleen-conditioned medium. A statistically significant increase in BM and spleen CFU-Meg was observed two days after the last administration of pGPL-Mc. This experiment points out the ability of pGPL-Mc to induce substantial stimulation of megakaryocytopoiesis and slight proliferation of stem cells in BM, but which is more pronounced in spleen. This molecule therefore appears to be a potential adjuvant of chemo- and radiotherapy in order to palliate the cytotoxic side effects of these cancer therapeutic modalities.