A randomized controlled trial of the value of oral adjuvant cytotoxic chemotherapy in the treatment of potentially curable breast cancer has been in progress in the Oxford Region since 1977. Eighty-seven patients were allocated to treatment with melphalan 0.2 mg/kg for 5 consecutive days every 6 weeks for 2 years; 98 patients were allocated to treatment with oral combination therapy consisting of melphalan 10 mg daily for 5 consecutive days, plus methotrexate 15 mg and 5-fluorouracil 250 mg on the first day, courses being repeated every 6 weeks for 2 years; and 88 patients were allocated to a control group which received no adjuvant chemotherapy. So far, 125 patients have suffered a recurrence of breast cancer and 85 have died. No statistically significant differences in outcome are apparent between the three treatment groups, although there is some indication of a beneficial effect of chemotherapy on disease-free interval in pre-menopausal women. Toxic effects of treatment, notably nausea, vomiting and bone marrow depression, have been moderately severe. In our view, the beneficial effects of current adjuvant cytotoxic chemotherapy, if any, are too modest to justify the suffering which such treatment can cause at a time when a woman with breast cancer might otherwise expect to feel physically well.