Women and children from 4 Guatemalan villages participated in a voluntary food supplementation program for 7 years. In 2 of the villages, they received a vitamin and mineral fortified, high-protein calorie supplement. In the other 2 villages, the vitamin-mineral fortified supplement contained no protein and a relatively small number of calories. Cognitive tests were administered regularly to children ages 3 to 7, and anthropometric measures obtained. In addition, measures of families' social milieu were collected at several points in time. Using multiple regression analysis, we find that both nutritional and social environmental measures are related to various dimensions of cognitive competence. The results suggest that nutritional intake, independent of social factors, affects cognitive development. There is also some evidence that the children who receive the high-protein calorie supplement (and whose mothers received it during pregnancy and lactation) are more likely to score high in cognitive performance. Our results, while not diminishing social environmental explanations of differences in cognitive function, suggest benefits from nutrition intervention programs in rural areas of lesser-developed countries.