The objective of this study was to evaluate the effects of raloxifene on normal breast tissue. A randomized, double-blind study was carried out in 30 ovulatory, premenopausal women of 18-40 years of age, who had been diagnosed with fibroadenoma of the breast. The patients were divided into two groups: Group A (placebo, n = 16) and Group B (raloxifene 60 mg, n = 14). The medication was given for 22 days, beginning on the first day of the menstrual cycle. An excisional biopsy was carried out on the 23rd day during which a sample of normal breast tissue was collected to evaluate the presence of the proliferating cell marker Ki-67. Student's t-test was used for the statistical analysis of data (p < 0.05). Mean percentage of stained nuclei in groups A and B was 10.96 +/- 1.27 and 1.21 +/- 0.26, respectively (p < 0.001). Raloxifene significantly reduced the proliferative activity of normal breast tissue in premenopausal women.