Tamoxifen (TAM), an antiestrogen was administered 20 mg b.i.d. to 20 patients with recurrent breast cancer at the time of first relapse who had been treated with the adjuvant therapy including TAM 10 mg b.i.d.. Patients who had been treated with TAM at least 1 year and in which the relapse had occurred after 3 months or more after the cessation of adjuvant treatment were enrolled in the study. Sixteen patients were evaluated, and a complete response was observed in 3 (19%), partial response in 1 (6%), no change in 5 (31%), and progressive disease in 7 (44%). The response rate was shown to be 25% with 95% confidence interval: 3.8-46.2%. The duration of response ranged from 23+ to 32 weeks. Patients who have received postoperative adjuvant therapy including TAM and have relapsed after the cessation of therapy may retain hormone dependency in responding to a further TAM treatment at the time of relapse of malignancy.