DESCRIPTION The outcomes of Helicobacter pylori infection in children are not well understood. Several epidemiologic studies have reported an association between H. pylori infection and growth retardation, suggesting interference with the nutritional process at critical periods of childhood development. Those studies were cross-sectional in design and cannot clarify the temporal relationship: does infection lead to retarded growth and development or do nutritional problems in childhood make the host more vulnerable to initial infection? This study will provide a prospective evaluation of the hypothesis that H. pylori infection leads to diminished growth in children, especially in minorities and underserved populations. A cohort of 360 Hispanic children of both sexes, ages 1-3 years, attending day care centers in Cali, Colombia, and negative for H. pylori infection by 13C Urea Breath Test (UBT) at baseline, will be followed for 2 years to monitor their growth with monthly measurements of weight and height. The incidence of H. pylori infection will be monitored with UBT every 3 months and by stool-H. pylori antigen retrieval test every month. The results are expected to establish the temporality of H. pylori infection and growth retardation, essential information for evaluating the effects of H. pylori infection on children's health and targeting appropriate preventive strategies.