In order to evaluate the mobilization of peripheral blood progenitor cells (PBPC) after an effective induction regimen in breast cancer, we performed a study on 15 breast cancer patients. Between January 1995 and June 1996, these patients received TNCF (THP-doxorubicin. vinorelbine, cyclophosphamide, fluorouracil for four days, every 21 days) with G-CSF support (5 microg/kg for 10 days after chemotherapy) to reduce aplasia. This regimen is known to result in a complete pathological response in 30% of patients. Between two cycles of TNCF treatment, hematological recovery was observed. Progenitor cells (CFU-GM and CD34+ cells) and mononuclear cells in DNA synthesis (MCDS) counts were performed daily, between the 12th and 17th post-chemotherapy days (81 samples). The results showed a similarity for hematological recovery and PBPC mobilization kinetics depending on the number of treatment cycles. The three methods used for PBPC evaluation were well correlated (P < 0.01) with an optimal mean PBPC recruitment by the last day of G-CSF administration: respectively, 11 520 (1729-26539) CFU-GM/ml of blood, 249 (14-1160) CD34+ cells/microl of blood and 211 (21-554) MCDS/microl of blood. These results suggested that a daily injection of G-CSF after one or two TNCF cycles will produce an effective PBPC mobilization in comparison with currently used regimens.