Twenty-seven cancer patients underwent peripheral blood stem cell apheresis during hematopoietic regeneration following induction high-dose cyclophosphamide (7 g/sqm; HD-CTX). Among these patients, eleven were also treated with granulocyte-macrophage colony stimulating factor (rhGM-CSF) for 14 days after HD-CTX. We describe technique, peripheral blood cell yields and side effects of 76 leukaphereses performed using a continuous-flow blood cell separator COBE 2997. Leukaphereses, carried out through 2-5 consecutive days per patient, were started significantly earlier in rhGM-CSF treated patients. In comparison to patients receiving HD-CTX only, administration of rhGM-CSF resulted in a significantly higher yield per leukapheresis of mononuclear cells and granulocyte-macrophage colony forming units (CFU-GM) (two-fold and eight-fold, respectively). Procedures were completed and well tolerated in all cases. Minor side effects were unfrequent. Our results suggest that rhGM-CSF accelerates hematopoietic recovery after HD-CTX and facilitates large-scale collection of peripheral blood stem cells utilizable for autologous transplantation.