Sucrase-isomaltase complex was purified from human intestinal mucosa. Immunostaining shows that sucrase-isomaltase is confined to the area of the striated cell borders of human small intestinal absorptive cells of the villus. Inhibition of sucrase and isomaltase activity by ethanolamine derivatives was investigated. Tris inhibits both types of enzyme activity and is the strongest inhibitor of the ethanolamine derivatives investigated. Bis-Tris inhibited sucrase more than isomaltase. On the other hand, mono-, di- and tri-ethanolamine were weak inhibitors of sucrase but not isomaltase.