The value of adjuvant endocrine therapy and adjuvant chemotherapy in improving the survival of patients with early breast cancer is still a subject of controversy after almost 40 years of clinical research in this area. The enormity of the adjuvant therapy literature is a challenge to the nonspecialist. The validity and importance of trial analyses often hinge on statistical methodology infrequently used by the clinician. For these reasons, this review is meant to serve as an easily accessible compendium of the large literature on the subject of adjuvant therapy and an intelligible guide around the pitfalls most often encountered in the analysis of this literature. The data utilized by the NIH Consensus Conference in September 1985 are summarized and the reasons for the conclusions reached by the consensus panel are both explained and extended. Trial data available through early 1986 justify the routine use of 6 months of adjuvant CMF in premenopausal women with histologically involved axillary lymph nodes. Postmenopausal women with histologically involved lymph nodes whose tumors also contain an estrogen receptor should routinely receive 2 years of adjuvant tamoxifen. In spite of promising preliminary reports, the treatment of all other patient groups and the use of other forms of adjuvant therapy must still be considered experimental.