In a controlled clinical trial, 52 patients with ER positive metastatic breast cancer were randomly assigned to receive initial treatment with either tamoxifen alone followed by sequential cyclophosphamide, methotrexate, and 5-fluorouracil (CMF) after tumour progression of concurrent tamoxifen plus CMF, All 52 patients entered are eligible and 50 patients were currently assessable. Response rates (CR + PR) were similar for the two treatment groups (15/24 tamoxifen alone, 17/26 tamoxifen + CMF). The median durations of survival for the two treatment groups 17.7 months and 17.1 months were also not significantly different. Significant correlations were found between level of ER and response rate and also between level of ER and response duration. From the result of this investigation it would appear that there is no advantage to the addition of chemotherapy prior to an adequate trial of hormone therapy in patients with metastatic ER positive breast cancer.