The duration of neutropenia and thrombocytopenia after high-dose chemotherapy has improved since the introduction of myeloid growth factors and peripheral blood progenitor cells (PBPC), yet there remains a subset of patients who have delayed hematopoietic recovery. Currently, there ar no established, reliable parameters which may be used to guide stem cell harvests. We investigated the utility of measuring harvested CD34 positive cell populations by flow cytometry. From March 1990 to July 1993, 30 women with advanced breast cancer underwent therapy with high-dose cyclophosphamide and thiotepa and stem cell rescue. Patients received either cyclophosphamide (CY) mobilized PBPC or CY/G-CSF mobilized PBPC. The number of harvested CD34+ cell and CFU-GM (colony forming units-granulocyte macrophage) were quantitated for each stem cell produce. There ar complete CD34 data for 21 patients and complete CFU-GM data for 20 patients. There was a significantly delayed neutrophil recovery in those patients reinfused with < 0.75 x 10(6) CD34+ cells/kg body weight (median days 22) compared with patients reinfused with > 0.75 x 10(6)/kg (median days 12, P = 0.0004); a similar trend was seen with platelet recovery (median 135 days vs 18 days, respectively, P = 0.002). With neutrophil recovery, there was no improvement in time to engraftment with a large number of reinfused CD34+ cells, but there was a trend towards shortened platelet recovery when the number of reinfused CD34+ cells exceeded 2.0 x 10(6)/kg (median 15 days) compared with CD34+ < 2.0 x 10(6)/kg (median 75 days, P = 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)