We have focused on defining the physiological factors giving rise to interpopulation variations in realized fertility in humans and the development of tools for assessments of these factors. This work has helped found the discipline of Human Reproductive Ecology which also includes examination of factors that link diet and disease status to such pertinent phenomena as birth seasonality, male endocrine function, and female conceptive loss. Exploration of the reproductive biology of a captive prosimian has expanded applications of our methods beyond humans. In vitro studies of the measurement and metabolism of several hormones including steroids, gonadotropins and inhibin and molecular genetic probing of disease vectors, immune status, female reproductive status, coital patterning, and urogenital microbial ecology in humans have expanded the variables available for study. We are poised to apply our methods to subjects in health and disease including chronic cystitis and cancer. Ultimately our work should help in diagnosis of fecundity and fertility and definition of which physiological and ecological parameters are most appropriate for modulation in programs meant to empower couples to regulate the size and spacing of children as well as those most vulnerable to insult and therefore in need of protection with environmental, animal management, public health, nutrition, or care delivery programs.