In an effort to identify etiologic agent(s) in ileitis and colitis, intestinal homogenates from patients with Crohn's disease and ulcerative colitis will be injected into footpads and peritoneal cavities of mice, and cultivated in parallel in tissue culture. The animals will be followed up to 2 years for development of granulomas and the tissue cultures will be examined for evidence of virus growth. Efforts will be made to agglutinate virus particles with autologous serum, and to correlate the results of granuloma transmission with virus production.