Sixty-six stage IV breast cancer patients received high dose chemotherapy followed by autologous transplantation of CD34-positive(+) cells obtained from the bone marrow and/or granulocyte colony stimulating factor (G-CSF)-mobilized peripheral blood. Grafts were examined for the presence of tumor using conventional histology and immunocytochemical staining. Patients achieved a granulocyte count of 500 x 10(9)/liter 10-12 days posttransplant, with a platelet count of > 20 x 10(9)/liter in 14-15 days. Enrichment of CD34+ cells from the peripheral blood progenitor cell (PBPC) collections resulted in a 1.3 to 4.0 log depletion of breast cancer cells from the graft.