SUMMARY OF WORK: PCBs, a family of industrial chemicals, and DDE, the most stable metabolite of the pesticide DDT, contaminate body fat and thus the fat in breast milk of human beings throughout the world. We have followed since birth a cohort of 900 children born between 1978 and 1982 in North Carolina, USA, to determine effects of prenatal and lactational exposure to PCBs and DDE. These children have no special chemical exposure. Samples of breast milk were collected throughout lactation and were analyzed for PCBs and DDE. We collected information on lactation duration, and thus we can estimate both transplacental exposure and exposure through milk. Starting in 1993, we sent annual questionnaires to the families asking the child's height, weight, and onset of menstruation (if female) and Tanner stage; we use a modification of the Tanner scale in which line drawings of secondary sexual characteristics appear as an ordered progression. Either the parents, the child, or both may send information. Children are followed until they reach the final Tanner stage, and, if female, have begun menstruation. In preliminary analyses, girls who had higher transplacental DDE exposure may mature earlier. Boys and possibly girls with higher DDE exposure have higher peripubertal body mass indices. In Taiwan in 1979, more than 2000 people were poisoned by heat-degraded PCBs. We have shown that, after 13 years of follow-up, the survivors have an increase in mortality from non-malignant liver disease; however, they do not yet show an excess of liver cancer, which is occurring in survivors of a similar poisoning in Japan in 1969. We continue to follow this cohort, including the children born to poisoned mothers. In North Carolina, about 2/3 of the children have reported their pubertal status to us. Preliminarily, girls with higher prenatal DDE exposure mature earlier, and boys with higher prenatal DDE exposure have larger body mass indices, but these findings have no adjustment for any potential confounders. In Taiwan, we are beginning design of a clinical and endocrinological study of peri-pubertal girls who were in utero when their mothers were poisoned by PCBs/PCDFs.