Release of mature cells from the bone marrow (BM) into the peripheral blood (PB) compartment is supposed to be triggered by changes in cell surface constituents, most probably in glycoproteins. The supposed importance of glycoproteins in marrow exit prompted us to investigate glycopeptides, i.e., the carbohydrate part of the cell-surface-located glycoproteins of isolated human bone marrow cells of the myeloid series at different stages of maturation. Fractionation of cells was performed by a four-step procedure, comprised of density gradient centrifugation and velocity sedimentation at unit gravity in specially designed separation chambers. With this method, promyelocytes/myeloblasts, granulocytes from bone marrow, and granulocytes from peripheral blood were isolated in high quantity with purities up to 90%, 90%, and 100%, respectively. Surface glycopeptides of the various myeloid cells were investigated by gel filtration analysis after metabolic labeling with radioactive fucose or after external labeling with periodate- borotritide under mild conditions. Within the normal myeloid maturation sequence, mature granulocytes within the bone marrow were found to transiently express altered surface glycopeptides, which disappeared after release into the peripheral blood. These oligosaccharide structures appeared similar to those encountered on leukemic blast cells, known as “cancer-related glycopeptides.” In contrast to normal granulocytes from BM, leukemic blast cells retained these aberrant carbohydrate structures on their surface after marrow release. A possible role for cancer-related glycopeptides in the process of marrow cell exit might be hypothesized.