One third of all breast cancers and two thirds of postmenopausal breast cancers are estrogen dependent. Antiestrogen strategies, such as inhibition of estrogen-receptor binding and estrogen deprivation, are effective for the management of hormone-dependent breast cancer. Although currently available agents are effective, the development of more potent and selective agents continues. Both steroidal and nonsteroidal inhibitors of aromatase have been developed for clinical uses. A novel class of steroidal irreversible antiaromatase agents demonstrates a high degree of specificity for the aromatase enzyme and exhibits a unique pharmacokinetic profile. The ability of these agents to inactivate aromatase may explain their high degree of potency and lengthy duration of action. Exemestane, an orally active aromatase inactivator, has demonstrated excellent selectivity and tolerability and broad-based efficacy in the treatment of postmenopausal breast cancer. Current findings suggest that exemestane will be a valuable alternative for women with breast cancer, not only for those progressing on other hormonal therapies but in earlier stages of the disease and prevention.