The objective of the proposed study is to elucidate the roles of genetic and environmental factors influencing childhood growth and development, with particular focus on gene-environment interactions. This will be done by establishing a longitudinal study of a large cohort of children in rural Nepal where parasitic gastrointestinal diseases are endemic. The proposed Jiri Growth Study is responsive to key programmatic goals in NIH PA-98-078, Genetic Architecture of Complex Traits, including support of new studies, expanding knowledge of genetic and environmental interactions, and increasing the quantity and quality of population-based data. The proposed Jiri Growth Study leverages resources created by the Jiri Helminth Project, a study of genetic predisposition to helminthic infection. The proposed Jiri Growth Study has four specific aims: Aim 1 is to collect at regular intervals from approximately 900 boys and girls a comprehensive battery of growth, maturation, body composition, and health status measures, as well as information on specific environmental factors that likely impact the growth and development of children in the study population; Aim 2 is to examine phenotypic associations between measures of growth, maturation, body composition and health status, and measures of parasite load, hematological status and household environment; Aim 3 is to use modern quantitative genetic methods to examine the genetic architecture of measures of growth, maturation, body composition, and health status taking into account specific environmental factors as covariates and/or interaction terms; Aim 4 is to use modern variance components linkage methods to determine the contribution of variation in quantitative trait loci (QTLs) linked to parasitic disease susceptibility to phenotypic variation in growth, maturation, body composition, and health status during childhood. Investigators on the proposed Jiri Growth Study have expertise in genetic epidemiology, auxology, medical sociology, population genetics, and physical anthropology. The proposed study will yield one of the largest familial databases ever collected of serial measures of the growth and development. When combined with the parasitic disease and household environment data to be collected, the proposed study will be unique in having the essential ingredients and statistical power needed to quantify GxE interaction effects on growth and development.