Sixty-nine patients with locally advanced breast cancer were given induction chemotherapy with doxorubicin and cyclophosphamide (day I ) followed by methotrexate and 5-Fu (day 8). Thirty-two of these patients were also given tamoxifen (days 2-6) in an attempt to induce a G1 arrest in cancer cells, and oestrogen (days 7-8) to stimulate proliferation and thus induce a synchronized wave of proliferating cells. The induction therapy response rate was 61% in the series as a whole (n = 69), but was found to be significantly better in the group on the tamoxifen/oestrogen synchronization regimen than in the remainder on chemotherapy alone (82%) vs. 43%). This difference was particularly marked in the respective receptor-positive subgroups [90% (Silo) vs. 30?4 (3/10); p < 0.0011. The findings suggest that, in combination with chemotherapy, tamoxifen/oestrogen therapy, given in the sequence outlined here, constitutes a promising regimen for the treatment of locally advanced receptor-positive breast cancer patients.