Although there is general consensus of greater prevalence of gastrointestinal (GI) distress in individuals with autism spectrum disorders (ASD), the nature of the link is unknown. There is preliminary evidence to suggest that GI distress in ASD may be associated with "Leaky-Gut" (i.e., increased permeability of the intestinal mucosal barrier due to either delayed or abnormal development), as shown by a study showing higher-than-normal prevalence in ASD children 4 - 16 years of age (e.g., D'Eufemia et al., 1996). During normal digestion, the mucosal barrier is responsible for keeping digestive enzymes out of the intestinal wall. Recent evidence shows that if these powerful degrading enzymes enter the wall of the intestine, they will cause major damage to the intestinal wall as well as inflammation in the brain. Investigators hypothesize that ASD may be associated with Leaky-Gut early in development, which combines, or interacts, with diet (breast-milk, formula, solid foods) leading to intestinal wall damage and inflammation in: 1) the intestine, which could explain the GI distress, and 2) in the bloodstream, which could reach and damage the developing brain, thus contributing to the onset of ASD itself. In this study, researchers will track key aspects of GI function in Low-Risk and "High-Risk" infants (i.e., infants who have an older sibling diagnosed with ASD), including: 1) signs of Leaky-Gut, 2) symptoms of GI distress (e.g., diarrhea, reflux, constipation), 3) diet (breast-milk vs. formula), and 4) evidence of digestive enzymes and inflammatory markers of cell death in the bloodstream. They will correlate GI, diet, and inflammatory measures with results from cognitive, visual, and behavioral tests, including standard ASD diagnostic tests, at two and three years of age to determine if Leaky-Gut is associated with the development of ASD.