A colonic villous adenoma removed from a glucose-6-phosphate dehydrogenase (G6PD) heterozygous patient was studied. The mucosal cells were separated to eliminate the contaminating nonadenoma cells by enzymatic disaggregation followed by isokinetic gradient centrifugation. The mucosal cells from this colonic polyp contained a single G6PD isoenzyme. Our study demonstrates clonality of this type of polyp and the value of the cell separation techniques in the experimental oncology. © 1982, American Medical Association. All rights reserved.