Thirty-two women who had developed loco-regional recurrence of breast carcinoma were entered into a controlled trial of adjuvant alpha-interferon. All patients had histological confirmation of recurrence, local treatment with radiotherapy and negative staging investigations. They were then randomized to either observation alone, or treatment with human alpha interferon 3 x 10(6) units subcutaneously daily for 1 year. There were no differences detected in the rate of local or distant relapse. With this lack of clinically significant efficacy and a high incidence of side effects, it is concluded that alpha interferon is of doubtful value in the adjuvant treatment of breast cancer.