A brief resume of adjuvant endocrine therapy for operable breast cancer is given. This was first suggested in the 1930's but has only become accepted in the last 10-15 years. The reason for the lack of survival benefit in the first randomised trial, which began in 1948 in Manchester, was thought to be due to the increasing use of hormone therapy for metastases. Revival of interest came with the survival gain reported in the Toronto ovarian trial and the success in post-menopausal patients of the non-toxic anti-oestrogen tamoxifen. The different dose schedules used in the various large tamoxifen trials could explain the confusingly variable results in the literature. Combined analysis of trial results indicates that CMF is the adjuvant therapy of choice for pre-menopausal patients but this therapy may in part be acting through the ovaries. The Scottish and NATO trials have an overall survival advantage from adjuvant tamoxifen, even in pre-menopausal patients, and both have shown results to be independent of oestrogen receptor (ER) status. Whether the extra 3 years given in Scotland adds an additional benefit over the more commonly used 2-year course is uncertain. A statistically invalid look at selected data in the Scottish trial suggests that, in ER positive cases, post-relapse tamoxifen may have as great an effect on total survival as adjuvant use, a finding similar to that suggested by the first ovarian ablation trial and one requiring continued review.