This study reports the results of measurement of alpha-tocopherol in erythrocytes and alpha-tocopherol/cholesterol ratios in patients treated with letrozol. Alpha-tocopherol in lipoprotein fractions and erythrocytes was determined by high-performance liquid chromatography in post-menopausal women with breast cancer treated with letrozol immediately before the start of treatment as well as 2 and 4 months later.