The purpose of this study was to develop a model system for detecting biological effects of gliadin which may be related to coeliac disease. The technique applied was tissue culture of chicken duodenum at several stages of fetal development. A normally occurring increase in disaccharidase activities in cultured tissue explants was diminished by the presence of peptic-tryptic digested gliadin or of a tryptic fragment of alpha-gliadin (alpha-GT 18,000). The effect of peptic-tryptic digested gliadin was only demonstrable in the early phase of fetal development (days 10-14), and disappeared at day 16. The release of enzymes into the culture medium was decreased by gliadin at the 12th day of fetal development. The results suggest that gliadin inhibits the differentiation processes of the fetal intestine.