The objective of our study was to evaluate the biologic role of granulocyte colony-stimulating factor (G-CSF) for hematologic reconstitution following autologous bone marrow transplantation (ABSCT). Using a commercially available enzyme-linked immunosorbent assay, serum levels of G-CSF were measured in samples from 48 patients (30 male/18 female) who underwent ABMT or ABSCT. Their median age was 34.5 years (range 16 to 51). Autografting was performed (40 ABMT, 8 ABSCT) in 23 AML, 8 ALL and 17 malignant lymphoma patients. Patients transplanted with blood stem cells had a faster leukocyte and neutrophil recovery compared with the ABMT patients (p < 0.025 and p < 0.05, respectively). During marrow aplasia G-CSF serum levels were elevated in all patients, with a median peak value of 2199 pg/mL (range 453 to 8676 pg/mL). A strong reverse correlation (R = -0.76, p < 0.01) could be demonstrated between G-CSF serum level and white blood count (WBC). An additional increase of G-CSF serum levels on days of fever (> or = 38.5 degrees C) or documented infectious disease was observed. During the early phase of marrow aplasia, the endogenously produced amounts of G-CSF reached concentrations which are used for in vitro stimulation of colony-forming unit granulocyte (CFU-G). The relationship between G-CSF serum level and WBC supports the central role of this circulating hemopoietin following myeloablative treatment and autotransplantation. During periods of higher demand such as fever and infectious complications, endogenous G-CSF production is enhanced.