Postoperative levels of steroid hormones have been measured in lymph and blood of 28 patients undergoing iridium implants as part of conservative treatment for operable breast cancer. The aim was to establish whether there were higher levels of hormones in lymph draining from necrosing tumour cells compared with peripheral blood levels. No differences were found in the ratios of estradiol, dehydroxyepiandrosterone sulphate or sex hormone-binding globulin in those patients with complete compared with incomplete excision of the primary tumour. However, premenopausal patients who had an incompletely excised primary tumour had increased levels of free testosterone in lymph draining from the tumour site on the third and fourth postoperative days. Thus androgens may have an important role in the intracellular metabolism of some breast cancers.