In a historical cohort study of 300,000 19-year-old men exposed to the Dutch famine of 1944-45 and examined at military induction, we tested the hypothesis that prenatal and early postnatal nutrition determines subsequent obesity. Outcomes were opposite depending on the time of exposure. During the last trimester of pregnancy and the first months of life, exposure produced significantly lower obesity rates (P less than 0.005). This result is consistent with the inference that nutritional deprivation affected a critical period of development for adipose-tissue cellularity. During the first half of pregnancy, however, exposure resulted in significantly higher obesity rates (P less than 0.0005). This observation is consistent with the inference that nutritional deprivation affected the differentiation of hypothalamic centers regulating food intake and growth, and that subsequent increased food availability produced an accumulation of excess fat in an organism growing to its predetermined maximum size.

Efforts to prevent heterosexual transmission of HIV (human immunodeficiency virus) infection have thus far focused on modifying sexual behaviors and the use of condoms. While the experience of family planners, particularly in those countries most threatened by heterosexual HIV transmission, has shown that the most effective measures of pregnancy prevention have relied on women, little attention has been given to barriers to HIV transmis-

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