Bone marrow aspirates from 28 healthy donors (18 adults, 10 children) were analysed by flow cytometry (FACS analyser) after purification of low density bone marrow cells (Ld BMC) on a density gradient (d = 1,077) and labeling with 23 anti-hematopoietic cells monoclonal antibodies. Based on physical properties the Ld BMC could be divided into four different populations called E, My, Mo et L including 13 +/- 8%, 33 +/- 15%, 12 +/- 5% and 42 +/- 14% of these cells respectively. The phenotypic analysis of these different populations allowed us to identify in E, erythrocytes (glycophorin A+, Rhesus D+ but negative for early erythroid differentiation markers like the transferrin receptor and/or the FA6-152 antigen); in My, the myeloid lineage (VIM2+, HLADR-); in Mo, the monocytic lineage (CD14+) and some myeloblasts (CD14-, VIM2+, HLADR+) and finally in L, an heterogeneous population including: 1) leucocyte cells, in which 27.3 +/- 9.0% are T cells labelled to the same extent by CD2, CD3, CD5 and CD6, 13.2 +/- 5.9% are B cells assessed by CD19 and CD20, 8.3 +/- 5.7% are Pré-B (CD10+), less than 5% are "natural killer" cells (CD16+ or Leu7+) and finally less than 6% are myelomonocytes (CD14+ or VIM12); 2) the erythroid lineage (Rhesus D+ = 43.7 +/- 12.9%, transferrin receptor and FA6-152+ 36.7 +/- 9.6%); 3) undifferentiated cells or progenitor cells (CD34+ = 6.5 +/- 3.5%); 4) cells unlabelled with any antibodies (approximatively 6%). We have not observed difference between adults and children bone marrow in regard to physical properties properties and all but also immunological markers. Indeed, a significant (p less than 0.02) higher proportion of B cells (CD19 and CD10) was observed in children. These data get from a large number of bone marrow could be used to quantify the imbalance of some bone marrow disorders.