In order to assess the progress of the growth of large intestinal polyps into cancer, the epithelial height and the size of the epithelial nuclei were measured. Mucin histochemistry was also carried out. The increase of the histologic grade was based on the extent of epithelial pseudostratification; epithelial height became greater and epithelial nuclei increased in size. The histochemical mucin values were as follows: the total amount of mucin in a given area increased in grade I epithelia in comparison with its behaviour in normal ones, and then decreased gradually with the increase in histologic grade. Neutral mucin became more conspicuous with the increase of epithelial pseudostratification. The amount of sulphated mucin decreased with the increase in histologic grade. In normal epithelia, sialomucin was rarely seen, but in grade I and II epithelia which did not show nuclear stratification the amount of sialomucin increased strikingly. It then decreased in amount with the increase in histologic grade. The noticeable increase of the amount of sialomucin in grade I and II epithelia can be thought of as a temporary phenomenon which appears in an early stage of carcinogenic process. The large intestinal polyps go through several stages before turning into cancer.