SEVERAL PERORAL BIOPSY techniques are now available which make it possible to repeatedly take samples from the small bowel. Sick individuals or normal volunteers can undergo this procedure with safety on an outpatient ambulatory basis. These so-called suction biopsies can be delivered from the biopsy site and fixed within seconds after excision, virtually eliminating autolysis, and thus providing tissue which is suitable for the most meticulous morphologic study by light or electron microscopy. This is a report of our experience in using the electron microscope for clinical investigation of the small bowel in man. The intestinal biopsies were obtained by peroral intubation with either our multipurpose biopsy tube,1which is activated by a pull-wire, or with our hydraulically activated biopsy tube.2Tissue samples so obtained were immediately fixed in osmic acid fixative,3,4dehydrated in graded strengths of alcohol or acetone and then embedded in methylbutyl methacrylate mixtures