Organochlorines, including pesticides (such as DDT) and industrial compounds (such as polychlorinated biphenyls, PCBs), are ubiquitous in the environment. All humans are exposed to low levels of these compounds. Exposure begins before birth, since the compounds cross the placenta, and continues throughout life. Assessment of human exposure to these compounds and evaluation of potential health effects of that exposure is essential to understanding what dangers, if any, these compounds may pose to humans. (1) We examined patterns of exposure to PCBs, looking both at patterns seen within a single population and at comparison of exposures across populations. (2) We looked for a relationship of maternal concentrations of several pesticides and PCBs to birthweight of their children, and saw none. (3) In addition, several studies of health effects of the DDT family of compounds are underway. These include examinations of the relationship of prenatal exposure to adolescent body size, of adult exposure to timing of menopause, and of prenatal exposure to anogenital distance (a sensitive measure of prenatal hormone exposure) in newborn boys.