The intestinal epithelium of the Baltic lamprey and its larva was studied. Glandular cells and absorbing cells simultaneously capable to synthesize polysaccharides were found histochemically in the composition of the epithelial layer. The cranial zone where glandular cells analogous to the cells of the pancreas were concentrated was revealed in the medial intestine of the larva. The rest of the intestine was devoid of specialized glandular cells. Using H3-thymidine as a precursor it was shown that in the cranial zone of the intestine the cambial cells were scattered diffusely throughout the whole epithelial layer and in other portions of the medial intestine the cambial zone was distinctly seen in the lateral portions of the intestine (the area of the fornix) where labelled nuclei were formed and mitoses took place. After injection of H3-thymidine poor incorporation of the isotope was found in the nuclei of solitary cells of some adult lampreys going to spawning. Uneven incorporation of S35-methyonine, used as a precursor, in the epithelium of the intestine and the liver of the adult lamprey was shown.