Endometrial cancer (EC) is estrogen-dependent tumor in the hormonal treatment of which mostly progestins are used. During last 5-7 years feasibility of aromatase inhibitors use in EC is discussed without any special practical move in this direction. To evaluate possible biological response of tumor and patients to such treatment, we conducted a short pilot study involving 10 primary postmenopausal EC patients, mostly stage Ia,b (average age 59) who received letrozole (Femara, Novartis) 2.5 mg/day during 14 days before operation. Clinical, sonographical, morphological, cytological and hormonal-metabolic (blood estradiol, FSH, LH, glucose, lipid fractions by RIA or enzyme-colorimetric methods; tumor progesterone receptors by LBA and aromatase activity by 3H-water release assay) studies were included into the protocol before and after treatment. Tolerability of letrozole was satisfactory in all patients. 2 patients reported decrease of pain and pathological secretions from uterine cavity. In 3 patients, decrease in M-sonographical endometrial signal was registered; average value after treatment was 31.1% lower than before it. Tendency to the decrease in estrogenicity of vaginal smears was revealed. Average decrease in blood estradiol was 37.8% and in progesterone receptor level and aromatase activity 34.4% and 17.5% respectively. Decrease of aromatase activity in tumor tissue was registered mostly in normal weight patients. A more detailed and longer randomized study of aromatase inhibitors in EC performed in neoadjuvant setting deserves consideration.