Background aims. We evaluated hematopoietic stem cells according to CD34 expression and aldehyde dehydrogenase (ALDH) activity in peripheral blood and apheresis product samples from patients after mobilization with granulocyte-colony-stimulating factor (G-CSF) alone or G-CSF after high-dose cyclophosphamide (4 g/m(2) once daily, intravenously on day 1). We also investigated the relationship between the number of SSClo CD45(dim) CD34(hi) cells, SSClo ALDH(br) cells and engraftment. Methods. Thirty patients (20 males and 10 females), who were candidates for autologous peripheral blood stem cell transplantation, were included in the study. Cyclophosphamide + G-CSF was used for 17 and G-CSF alone for 24 mobilizations. Primary diagnoses were multiple myeloma (n = 14), Hodgkin's lymphoma (n = 7), non-Hodgkin's lymphoma (n = 2), acute myloid leukemia (n = 2), chronic lymphocytic leukemia (n = 1) and germ cell testis tumor (n = 1). Results. Numbers of SSClo CD45(dim) CD34(hi) cells and SSClo ALDH(br) cells were highly correlated in both peripheral blood and apheresis products (P < 0.001). We could not find a relationship between the transplanted SSClo CD45(dim) CD34(hi) cell dose or SSClo ALDH(br) cell dose and platelet or neutrophil recovery. The optimal thresholds for SSClo CD45(dim) CD34(hi) cells were 5.40 x 106/kg for neutrophil recovery and 7.22 x 106/kg for platelet recovery. The optimal thresholds for SSClo ALDH(br) cells were 6.53 x 106/kg for neutrophil recovery and 8.72 x 106/kg platelet recovery. Conclusions. According to our data, numbers of SSClo ALDH(br) cells are in very good agreement with numbers of SSClo CD45(dim) CD34(hi) cells and can be a predictor of stem cell mobilization.