There exists substantial epidemiologic and experimental evidence that diet affects risk of breast cancer. It has been postulated that dietary factors act through alterations in the hormonal milieu, especially in the teenage years when the breast is thought to be particularly sensitive to carcinogens. Previous cross-cultural studies of hormone levels in women on different diets have yielded inconclusive results. Those studies, however, have focused on comparisons of total serum estrogens and androgens. The proposed study will examine levels of unbound and albumin-bound serum estradiol and testosterone, as well as ovulatory status, in two groups of postmenarchial teenage girls. One group is composed of 110 boarding school Seventh-Day Adventists who ingest lacto-ovo-vegetarian diets; the other group is composed of 125 non-vegetarian girls in another boarding school in the Chicago area. Dietary intake will be documented with seven-day food records and measurements will be made of the following hormones: total, albumin-bound and free estradiol; total, albumin-bound and free testosterone; and steroids bound to sex-hormone-binding globulin on both day 10 or 11 and day 22 or 23 of one menstrual cycle. Ovulatory status will be determined from one day 22 or 23 serum progesterone and two urine pregnandiol specimens between days 20 and 24 from each of six cycles. Measurements will also be made of possible confounding variables such as age at menarche, time since menarche, medication use, height, weight, skinfold thickness, and physical fitness level. In addition to group comparisons, analyses will be performed within each group of girls examining the relationships between each hormone level and dietary variables which have been implicated as affecting risk of breast cancer. Should significant group differences in hormone levels be found, the results of the proposed study will be used as the basis of an intervention trial at one of the boarding schools to study the effect of dietary change on hormonal balance.