Adjuvant systemic treatment delays relapse and prolongs survival in patients with operable breast cancer. However, the relative wealth of available agents and the heterogeneity of the target population contribute to considerable uncertainty about the optimal approach to particular patient groups. Systematic review and meta-analysis of the results of trials testing polychemotherapy have clearly established the value of such treatment. Endocrine treatment with tamoxifen was to be especially useful in patients with hormone-receptor positive tumours. Research in recent years has therefore concentrated on secondary questions, such as scheduling, dose intensity and new combinations of chemotherapeutic agents. Combined chemo-endocrine treatments, using polychemotherapy plus tamoxifen, ovarian ablation or both, have been compared with either modality alone. Other endocrine agents such as fluoxymesterone acetate, medroxyprogesterone acetate and, recently, LH-RH analogues have also received attention. The systematic review presented here suggests that combined cytotoxic and endocrine therapies might be the most effective use of available treatments for most, if not all, patients, and highlights the unresolved questions requiring further research.