Menopause is a biologic marker of aging common to all women. The association between local ecologies and hormone levels in women of reproductive age is well established (Ellison 1994; Nuñez de la Mora et al. 2007): women who live in a nutrient-poor environment tend to have lower levels of reproductive hormone than women who mature in richer environments. There also are differences in how women experience menopause across populations and cultures (Obermeyer and Sievert 2007; Sievert et al. 2007). Are these two findings associated? The overarching hypothesis of this study is that the intensity of uncomfortable symptoms experienced during the menopausal transition is positively correlated with the steepness of the decline in ovarian hormone levels. We test this hypothesis in two populations that differ in genetics, SES, and lifestyles: the Toba, an indigenous community in the province of Formosa, Argentina, and non-indigenous upper middle-class women in the city of Formosa. Specific aims are to: (i) collect anthropometric and hormonal data from a cross-section of peri-menopausal and menopausal women in each of the two settings to establish baselines for physical and physiological changes during and after the transition; (ii) collect qualitative data on the experience of menopause in each of the two populations; and, (iii) monitor hormonal changes and symptoms during the menopausal transition in a subset of women over a 1-year period.