PIP: Population control among the Yanomamo tribe of the Amazonian tropical rainforest is studied. 25% of male deaths are due to warfare. A male-female balance is achieved by the practice of infantcide, especially among female infants. The male:female ratio among the under-15 age group is 135:100, belying the tribe's contention that neither sex is more likely to be killed than the other. The major population controlffactor, however, is disease with about 54.2% of adult deaths due to malaria, and other communicable disease accounting for 11.7%. Other population controls are abortion and postnatal sex taboos, although the latter is for the most part overruled by the practice of infanticide for any child born while a previous child is still nursing. The intense intervillage warfare is increased by the shortage of women, resulting from female infanticide combined with polygamy and marriage alliances in which even unborn females are promised. Because there is war, male children are preferred and the cycle continues. Other observers, however, feel that the constant warfare is part of the need for new garden sites brought about by reliance on slash and burn agriculture. The author believes the shortage of women is just a side effect of population control occasioned by a protein shortage.