Forty children between the ages of 16 and 42 months and their mothers, living in an Ethiopian rural village, participated in the study. The objective was to determine the mental development of the children using the Bayley Scale of Mental Development, and to examine its relation to nutritional status and mother-child interaction. Forty-eight percent of the children were mildly or moderately malnourished; 7.5% severely so. The child's weight for age was significantly related to the child's scores on the Bayley scale. Mother-child interaction was assessed through a 30-60 min observation of the pair in a naturalistic setting around the home. The number of verbal, gestural and motor actions spontaneously initiated by the mother and child, as well as responses made by each to the others' behavior were recorded and coded separately. The rate of a mother's verbal responses to the child positively predicted the child's verbal score. In contrast, the mother's spontaneously initiated motor actions toward the child correlated negatively with the child's performance score. The mother's responsiveness was unrelated to the child's nutritional status, age or sex, but was best predicted by a fussing/crying child and by her expectations about the ages when specific social-cognitive abilities would be acquired by a child.