Extracts of human stomach mucosa were shown to contain immunoreactive intrinsic factor and small amounts of R protein and transcobalamin II. In gel filtration the mucosal vitamin B12-intrinsic factor complex behaved as though its molecular weight were smaller than the corresponding complex in gastric juice. In isoelectric focusing both the gastric juice and mucosal vitamin B12-intrinsic factor complexes resolved into numerous isoproteins. These findings were verified by DEAE-cellulose chromatography. The mucosal intrinsic factor isoprotein pattern contained, in addition to the isoproteins found in gastric juice, components with higher isoelectric points -- that is, pH 5.73-6.64.