Transgenic mice carrying erbB2(HER-2)neu gene are characterized by high incidence of mammary adenocarcinoma. The content of estrogen receptor was no more than 10 fmol/mg protein in 8 of 14 studied tumors, while the content of progesterone receptors was even lower in all 14 studied tumors. Based on these data, we distinguish two subtypes of HER-2/neu-adenocarcinomas in mice: ER+,PR- and ER-,PR-, which can be used for the development of new approaches to the treatment of receptor-negative mammary gland tumors.