Lymphedema and arm swelling after surgery and/or radiotherapy for breast cancer is a major complication in about 30% of breast cancer survivors. When this occurs in premenopausal women, a hypothesized complicating factor is a sex hormone related increase in interstitial fluid volume, that we believe causes hormone-dependent increases in arm tissue water that exacerbates the edema of the lymphedematous limb. Such effects have important implications for therapy and skin blood flow. Our goal is to test this hypothesis in healthy premenopausal women to determine the extent of sex hormone impacts on arm tissue water, volume and skin blood flow, and to compare these parameters to those obtained in postmenopausal women, in whom both estrogen (E) and progesterone (P) values are much reduced. To accomplish this, arm tissue water, volume and skin blood flow will be measured at three time points during the menstrual cycle in 30 premenopausal women. The time points will be on cycle-day 4 (low E and low P), cycle-day 12 (high E and low P), and cycle-day 22 (high E and high P). Values of E and P will be determined with saliva assays. Day 4 parameter values will be compared to those obtained from 15 postmenopausal women. This study's significance relates to its potential to provide a foundation to develop rationally based new or modified strategies to treat lymphedematous limbs in premenopausal women. Without this initial study of normal limbs, investigations of lymphedematous limbs would not be scientifically based. In addition to its potential relevance to lymphedema, this study will provide a basic physiological characterization of the relationship between premenstrual hormone changes and tissue water content. The significance of the pre- versus postmenopausal comparison relates to the quantitative information that will emerge regarding the role of hormones in age-related changes in skin moisture and blood flow.