Aromatase inhibitors used in breast cancer, are drugs that inhibit the transformation of androstenedione and testosterone, respectively in estradiol and estrone. Two classes have been described: steroidal inhibitors which act competitively and irreversibly and non steroidal inhibitors which block the P 450 cytochrome. The first one is aminoglutethimide which has an adrenal effect on 11, 18 and 21 hydroxylase. Rogletimide, less powerful and less specific is a aminoglutethimide analogue. The response rates obtained with formestane is not different. The clinical development has been stopped due to a lack of specificity. Letrozole, vorozole, exemestane and anastrozole are more powerful and more specific. Letrozole and vorozole are at least as efficient and better tolerated than aminoglutéthimide. Anastrozole, letrozole and vorozole are at least as efficient as megestrol acetate and better tolerated in advanced breast cancer patients receiving a second line hormone therapy.