A significant proportion of patients with hematologic malignancies fail to mobilize sufficient hemopoietic progenitor cells (HPC), thereby restricting wider application of autologous transplantation. It would be of considerable use to develop a test that could be used prospectively to assess an individual patient's capacity to mobilize HPC. Twenty-two patients with lymphoma, myeloma, and chronic lymphocytic leukemia were given a single dose of 12 microg/kg SC of granulocyte colony-stimulating factor (G-CSF). Blood colony-forming unit granulocyte-macrophage (CFU-GM) and CD34+ cells were scored prior to the test dose, and 72, 96, and 120 hours later. The patients were then mobilized with a standard cyclophosphamide and G-CSF regimen and had blood stem cells harvested. Patients were categorized as good, poor, or intermediate mobilizers on the basis of the CFU-GM/CD34+ cell harvest content and the number of aphereses required to reach established threshold counts. The outcome of cyclophosphamide/G-CSF mobilization was correlated with the response to the test dose of G-CSF. Good mobilizers had significantly higher peak CFU-GM values and CFU-GM increment in response to the test dose of G-CSF compared to intermediate and poor mobilizers. A peak CFU-GM count of > or = 250/mL identified the good mobilizers; conversely, all poor mobilizers had a peak CFU-GM count of <102/mL. An increment in CD34+ cells counts of > or = 2.5/microL was only observed in good mobilizers. The "G-CSF" test is a reliable test that can be used successfully for the assessment of mobilizable HPC in patients with hematologic malignancies. It can also be used to stratify patients enrolled in trials of mobilizing agents.