Recent research suggests that oestrogen may play an important role in cognition. Epidemiological and experimental studies of hormone replacement therapy in post-menopausal women suggest that oestrogen may be important to verbal memory in particular, as well as other cognitive functions such as attention and processing speed. Some studies have also suggested that HRT may have a beneficial effect for Alzheimer's disease, both in the prevention or delay of onset and that it is also of therapeutic benefit to patients in whom the disease is established. The use of selective oestrogen receptor modulators (SERMs) and other hormonal therapies for the treatment of breast cancer is common, yet few studies have examined the possible cognitive effects of this form of treatment. Several studies have shown cognitive decline in women receiving treatment for breast cancer, but the focus has been on the effects of chemotherapy. Further confusion has resulted from the diverse methodologies used in the existing literature. A pilot study to develop a suitable cognitive battery of tests for the evaluation of cognitive function in women receiving hormonal therapy for the treatment or prevention of breast cancer is introduced.