The incidence of low birthweight is high for Blacks and Puerto Ricans in the U.S. relative to White Anglos, Mexican Americans, and Native Americans. The Black-White difference in birthweight remains large even when maternal age at birth, birth order, marital status, and education are controlled. Income often is mentioned as a likely cause, although other groups with low income (e.g. Mexican Americans, Native Americans) have favorable birthweight distributions. The negative effects of income in these other groups may be offset by other, more favorable characteristics; clearly a multivariate approach to explaining birthweight differentials is needed. The purpose of the proposed research is to construct a causal model of birthweight, proximate determinants, and socioeconomic characteristics, and to use this model to explain similarities and differences in birthweight among Blacks, Mexican Americans, Native Americans, Puerto Ricans, and White Anglos. The proximate determinants include indicators of stress, nutritional status and physical size of the mother, smoking, and prenatal care. Socioeconomic characteristics include income, age, marital status, education, etc. Income is a central focus of the model. Survey data will be used to measure family income in considerable detail. Many high-risk groups live with relatives and receive various types of assistance from relatives, as well as various types of public assistance. Household income, kinship assistance (with housing, finances, and child care), and public assistance will all be considered along with family income. Proximate determinants are included in the model in order to explain racial and ethnic differences in birthweight in medical/biological and policy- relevant terms, and in order to trace the causal mechanisms by which income and other socioeconomic characteristics are associated with birthweight. The research will use data from the National Longitudinal Survey of Work Experience of Youth for a nationally representative sample of 4,000 babies born to mothers aged 14-29.