This project seeks to develop new statistical methodologies for problems in human development and to apply existing methodologies to those problems in novel ways. Work continues in two areas: (1) statistical modeling of the distribution of birthweights in human populations, and (2) statistical modeling of serum concentrations of reproductive hormones in peripubertal children, (The second area of work will be curtailed since an important collaborator, Dr. Penelope K. Manasco, left NIEHS at the end of June). Development of a satisfactory statistical model for the distribution of birth weights in a population will facilitate a refined understanding of the relationship of birthweight to infant mortality. We have developed both a model and a method for fitting the model to data which permit a parsimonious description of a birthweight distribution, a description which should be useful in investigating social and environmental influences on birthweight. Serum profiles of pituitary gonadotropins and gonadal hormones exhibit distinct peaks with irregular spacings. With an appropriate statistical model, one could describe these profiles with few parameters, allowing comparisons among subjects with normal and abnormal pubertal development and providing insight into mechanisms of dysfunctional development. We are evaluating a few models for adult or animal profiles for particular hormones to see whether they provide adequate descriptions for a variety of hormones in prepubertal children, but we have not yet found a model that performs well across several hormones.