Evidence and hypotheses concerning the relationships between health and nutrition factors in the family and fertility outcomes are examined in order to determine direct or indirect causal relationships. A review of evidence concerning the biological and behavioral effects of nutrition and health factors of fecundity and fertility, is followed by a description of an integrated model of relationships among nutrition, health, and intervals between birth in individual households. The model predicts changes in fertility that result from changes in nutrition and health, and illustrates statistical pitfalls in such research. Finally, an approach to understanding poor people's health and nutritional behavior, and the implications of the available evidence for choosing among modes of delivering health, nutrition and family-planning services is considered. Research questions which help to identify areas for intervention are also suggested. (CM)