High-dose myeloablative chemotherapy supported by peripheral blood progenitor cell (PBPC) transplant is rapidly replacing bone marrow transplant to treat a number of chemosensitive cancers. Numerous investigators have studied the relationship of CD34+ cell dose and engraftment kinetics in an effort to help define minimum and optimum target stem cell doses. A number of studies suggest that reinfusion of > or = 5 x 10(6) CD34+ PBPCs results in prompt and durable platelet engraftment. Mobilization of stem cells can be accomplished through use of chemotherapy alone, colony-stimulating factors, or a combination of the two. Strategies to improve PBPC yields include filgrastim in combination with chemotherapy or with other hematopoietic growth factors. In this paper, the advantages and disadvantages of these strategies will be discussed, and the results of a recently conducted, randomized, controlled phase 3 clinical trial in breast cancer patients receiving either SCF plus filgrastim or filgrastim alone for PBPC mobilization will be reviewed.