It has been implied that fat and fiber intakes influence breast cancer risk. The effects of these dietary factors may be mediated by hormonal changes. We evaluated the relationships between fat or fiber intake and serum concentration of estradiol (E2) or sex hormone-binding globulin in premenopausal women. In 1994 blood samples were collected from each of 50 premenopausal healthy Japanese women on Days 11 and 22 of the menstrual cycle. Nutrient intakes were assessed by food frequency questionnaire in which the subjects were asked about their diets during one year before the study. Each nutrient intake was categorized into tertile after adjustment for total energy. Linear regression models, including age and cycle length as covariates, were utilized to evaluate the association between the nutrient intakes and the hormone concentrations. A statistically significant trend was observed between increasing fat intake and increasing E2 on Day 11 of the cycle (p = 0.05). The positive trend for increasing sex hormone-binding globulin on Day 22 with fat intake was of borderline significance (p = 0.06). There was a statistically significant inverse trend for E2 on Day 11 of the cycle with fiber intake (p = 0.05). It was suggested that fat as well as fiber intake should affect the hormone status.