Formestane (Lentaron) and anastrozole (Arimidex) are in clinical use as second-line treatments for advanced breast cancer. Current practice is often to use an aromatase inhibitor only once before switching to third-line agents such as progestins. There are few clinical data on the sequential use of aromatase inhibitors. We therefore decided to study the clinical effects of anastrozole in postmenopausal patients with advanced breast cancer who had already received formestane. 21 patients were recruited. When receiving formestane 2/21 (10%) achieved a partial response (UICC criteria) and 10/21 (48%) stable disease. Of these 12 patients, 9 achieved further stable disease on anastrozole (78%; 7/9 oestrogen receptor positive). 4 of 9 patients who progressed on formestane also stabilised on anastrozole, of whom 3 had oestrogen receptor positive breast carcinomas. The explanation of this second stabilisation may relate to a further fall in oestradiol levels. We feel these results are of interest and warrant further clinical investigation.