To support multicyclic, dose-intensive chemotherapy in breast cancer, we assessed the effects of reinfusing hematopoietic progenitors either as a leukapheresis product or as mobilized unprocessed whole blood. In this clinical study, 16 consecutive female breast cancer patients were given six cycles of chemotherapy regimen EC (epirubicin (150 mg/m2) and cyclophosphamide (1250 mg/m2) on day 1). In the first cycle, 24 h after chemotherapy, mobilization of the peripheral blood progenitor cells (PBPC) was started with growth factor G-CSF (Neupogen; Amgen-Roche) at a dose of 5 microg/kg/day for 13 days. In all other cycles G-CSF had been given at the same dose from day 7. On days 11, 12 and 13 the leukaphereses were performed and their products cryopreserved. On day 14 whole blood was collected. The median peak incidence of CFU-GM (granulocyte-macrophage colony-forming unit) in peripheral blood was approximately 50 times the baseline level. The leukapheresed PBPC were divided into portions and reinfused after the fourth, fifth and sixth chemotherapy courses. The support with mobilized whole blood was given after the second and third cycles. The effects of the support of whole blood vs leukapheresed PBPC on hematopoietic recovery were compared. The best yields of leukaphereses were achieved on day 13 after initiation of the chemotherapy. The mean number of CD34+ cells was 4.93 x 10(6)/kg (s.d. 2.7; range 0.36-10.54 x 10(6)/kg) the amount of CFU-GM was 2.18 x 10(5)/kg (s.d. 1.3; range 0.07-4.2 x 10(5)/kg). The yields of CFU-GM in 450 ml whole blood collected on day 14 reached 0.51 x 10(5)/kg (s.d. 0.28; range 0.05-1.5 x 10(5)/kg) and of CD34+ cells were 1.3 x 10(6)/kg (s.d. 0.8, range 0.18-2.58 x 10(6)/kg). PBPC yields in 450 ml of unprocessed whole blood were in some cases not sufficient for good hematopoietic recovery after the EC cycles. Grade 4 leukopenias and thrombocytopenias were two times higher in cycles with whole blood support than in cycles with cryopreserved PBPC support. An increase of PBPC harvest can be simply achieved by collecting larger amounts of unprocessed blood, as used by some authors.