The International Breast Cancer Study Group (IBCSG, formerly the Ludwig Group) is currently conducting several trials to improve available adjuvant therapies for operable breast cancer. Within the framework of clinical trials, treatment is available for several subpopulations of patients with operable disease. Two trials for patients with node-negative breast cancer question the efficacy of the combination of chemotherapy and endocrine manipulation. Four trials for patients with node-positive disease investigate questions of chemoendocrine therapy and of delayed reintroduction of chemotherapy after an initial cytotoxic treatment. One trial for elderly patients investigates the role of axillary lymph node dissection in terms of treatment outcome and quality of life. The ongoing trials are based on the results of past investigations by the Group: seven clinical trials, conducted since 1978, tested hypotheses of timing, duration, and the combined use of chemo- and endocrine therapies. Several ancillary studies were conducted using the database amassed from these trials, including pathological findings in node-negative disease, significance of micrometastases detected by serial sectioning of axillary nodes, importance of c-erbB-2 oncogene expression for prediction of treatment responsiveness, patterns of relapse, and assessing the impact of adjuvant treatment for breast cancer on the patients' quality of life. This report presents updated results of the seven IBCSG trials conducted from 1978 to 1993 and describes the trials currently open to patient accrual.