AbstractThe distribution of carbonic anhydrase activity in the intestinal tract of the guinea‐pig was studied by the histochemical method of Hansson. Enzyme activity was demonstrated in epithelial cells, erythrocytes and capillary walls. In the gastric mucosa parietal cells, surface mucous cells and neck mucous cells were highly active. In the small intestine only a few epithelial cells on the villi and in the upper part of the crypts showed enzyme activity. They seemed to be randomly scattered among inactive ones. It is not clear at present if they represent a distinct cell type or specialized absorptive cells. In the proximal colon most surface epithelial cells were highly active (goblet cells were inactive), whereas the surface cells in the distal colon showed less activity with a more varying degree of staining. In the cecum enzyme activity was found in the surface epithelium and in the upper part of the crypts, the staining being most marked at the luminal border of the surface cells. The staining reaction was completely inhibited in all tissues by 10 μMacetazolamide, except for the luminal staining of the cecum, which was inhibited only by 100 μMacetazolamide. This indicates the presence of high concentrations of carbonic anhydrase, probably of the “low activity” form, at this locus. Mucosal scrapings were taken from the intestinal tissues, homogenized and assayed for carbonic anhydrase activity by a changing‐pH indicator method. The results confirm those of previous studies and correlate well with the histochemical