From a material derived from routine investigations, 40 gallbladder specimens were selected in which metaplastic cells had been observed. All the cholecystectomies were performed for gallstones. Of the patients 6 were male and 34 female. The mean age was 51.2 years. 36 specimens revealed goblet cells, enterochromaffin cells were found in 22, antral-type (pseudopyloric) glands in 23 and islands of gastric surface epithelium in 15 specimens. Histochemical methods to visualize sulphated, non-sulphated acid and neutral mucins were used. Ordinary gallbladder epithelium showed a predominance of sulphated mucosubstance. Sporadic goblet cells usually occurred in so-called goblet cell areas which, if small, were located in the tops of folds and only when larger also in the deeper parts of folds. As the goblet cell area enlarged, the relative proportion of sulphated mucin diminished and correspondingly non-sulphated acid mucin increased, while neutral mucin was noted both in the goblet cells and in the intervening columnar cells. In 20 specimens there were enterochromaffin cells in the goblet cell areas while only 2 specimens revealed enterochromaffin cells outside the goblet cell area. The glands outside the neck region of the gallbladder resembled gastric antral glands in their general architecture and in the appearance of individual cells. A part from frequent enterochromaffin cells (in 12 specimens) the glands are composed of mucous cells. The glandular cells contained sulphated mucin, non-sulphated acid and neutral mucin chiefly in the peripheral parts of glandular cells. In the gallbladders there were numerous abnormalities in some areas: heavy mucous secretion, goblet cells, enterochromaffin cells and superficial gastric-type epithelial spots were seen chiefly in the upper parts of folds, while proliferation of antral-type glands occurred in the basal parts. It is probable that some common pathological factors are responsible for the frequent simultaneous appearance of different types of metaplasia.