There is no longer any doubt that the inherited genetic constitution of the individual has a large influence on the entire life cycle, from human fetal development and pre- and postnatal growth to subsequent health status. However, growing evidence suggests that this predisposition is not rigid, but that early genetic imprinting, caused by exposure to a diverse spectrum of nutrients, macromolecules, microbial agents and other cellular or soluble components present in the external environment, is also of importance. According to this concept of the developmental origins of adult diseases, intrauterine and early life events play an important role in the etiology of human diseases: there seems to exist a critical >window of opportunity' in the human infant before and during pregnancy, and up to 24 months of age. Altered exposure to different environmental agents during this critical period may determine the nature of responses in the perinatal period, and the expression of specific disease states in later life. The papers presented in this publication thus focus on the impact of perinatal growth, nutrition, environmental microflora, and host immune responses on the outcome of health and disease in later life.