Investigators hope to learn to characterize human intestinal microbial communities (microbiome: the collection or collectivity of microorganisms) using molecular methods, examine the mechanisms of interaction between host and microbiome using genomic approaches, and determine how the microbiome both preserves local health and promotes pathology. Investigation will focus on primary sclerosing cholangitis, biliary atresia, as well as states of health. The composition of the associated microbiome will be assessed based on ribosomal DNA and RNA sequences, and attention will be given to richness (diversity), evenness (relative abundance), and variation with respect to time, person, and anatomic niche. Host response at the adjacent mucosal surface will be assessed based on genome-wide gene expression patterns. In addition, changes in the metabolites of the blood will be analyzed.