Peripheral blood stem cells (PBSC) can be used for hematopoietic reconstitution in patients who have received high-dose chemotherapy (HDC). Previously, we reported 18 such patients who had nonmobilized PBSC harvested in steady state. We have now performed PBSC reinfusion in 24 patients with hypocellular or tumor-involved marrow who received cyclophosphamide (Cy) mobilization (4 grams/m2) prior to PBSC collection. The PBSC were collected upon rebound hematopoietic recovery by continuous-flow leukapheresis and subsequently cryoproserved. A median of 3.17 x 10(8) mononuclear cells/kg (range 1.47-3.95 x 10(8)) were collected. Patients underwent a median of 6 apheresis procedures (range 5-12). To date all 24 patients have undergone PBSC reinfusion after HDC. Fourteen patients received post-reinfusion granulocyte/macrophage colony-stimulating factor. Granulocyte recovery (> 500 x 10(6)/ml) has occurred at a median of 13.5 days (range 7-39) and platelet recovery (> 50 x 10(9)/ml without transfusion support) has occurred in 20 patients at a median of 33 days (range 7-121 days). Four other patients have platelet counts of greater than 20K and are transfusion independent, but have still not achieved counts of 50K. PBSC collection after Cy mobilization is feasible and effective for hematopoietic reconstitution after HDC and reinfusion. All 24 patients demonstrated trilineage engraftment. Although neutrophil recovery was not significantly hastened (as compared with our nonmobilized or steady-state data), time to platelet engraftment was foreshortened.