The expression of differentiation antigens (D/As) and adhesion molecules (A/Ms) was studied on CD34 positive (CD34+) cells in peripheral blood (PB) and bone marrow (BM) of patients treated with myelosuppressive chemotherapy followed by granulocyte colony-stimulating factor (G-CSF) administration (CT/G-CSF). CD33 positive rates of PB and BM CD34+ cells were significantly higher in the patients than those in the normal controls. CD49d positive rate of PB CD34+ was significantly lower than that of BM CD34+ cells in both the patients and the normal controls, and this decreased expression of CD49d on PB CD34+ cells was larger in the patients than in the normal controls. CD117 positive rate was significantly lower in PB CD34+ cells of the patients than that of their BM CD34+ cells and PB CD34+ cells of the normal control. These results suggested that more mature progenitor cells increased in the patients' PB and BM after CT/G-CSF, and that the decreased expression of CD49d played an important role on peripheralisation of CD34+ cells even in steady state, and the decreased expression of CD117 was related with the mobilization of CD34+ cells after CT/G-CSF. CT/G-CSF decreased the expression of CD117 and enhance the decrease of CD49d expression on PB CD34+ cells. These changes appeared to be involved in the mobilization mechanism of hematopoietic progenitor cells from BM into PB after CT/G-CSF.