Despite its limitations conventional microscopic examination of jejunal biopsy material is still one of the most tangible approaches to the investigation of small-intestinal malfunction. The biopsy specimens produced by the various modem flexible instruments are adequate, although small and need careful technical processing if maximum information is to be obtained. Suffice it to say that rapid fixation and the minimum of handling which ensures that sections are cut at right angles to the mucosal surface are essential. The avoidance of tangential cutting artefacts and an examination of several or serial levels throughout the biopsy ensures that truly representative morphology is seen in each specimen.Stereoscopic examination while the biopsy is in fixative can also be helpful and gives preliminary information which later can be correlated with the histology, but it should never take the place of a proper histological examination. The extra handling and the wiping away of adherent mucus in order to achieve a good dissecting microscopic view should be avoided because of the inevitable distortion, smearing, and crushing artefact which it may cause. Frequently the net result is a loss of much more information than is gained by the stereoscopic study.In the detection of morphological abnormalities it is mandatory that the observer is acquainted with the normal and, in particular, its variations. The morphology of the small intestine varies along its length, and the normal proximal duodenum not infrequently shows an increased number of stunted and leaf-shaped branching villi when compared with the jejunum. Brunner's glands, traditionally thought to be localized to the duodenum, have a marked variation of distribution often extending to the jejunum, particularly in children (Landboe-Christensen, 1944). Hyperplasia or undue prominence of Brunner's glands is often associated with obvious villous stunting. Biopsies from the proximal duodenum not infrequently show an increased inflammatory cell infiltration with villous atrophy and superficial epithelial degenerative changes which are independent of changes in the remainder of the duodenum and jejunum. Similar appearances are seen in the immediate vicinity of gastrojejunostomy stomas and are probably more closely related to local factors, including hyperacidity and gastric dysfunction. As the ileum is approached the ratio of goblet cells to absorptive cells increases and the villi tend to become broader and shorter than in the jejunum. The number of lymphoid aggregates increases distally and sometimes proximally they are conspicuous. Villi overlying lymphoid areas are often stubby and may be absent.Villous architecture is determined in part by the depth of tissue obtained at biopsy. When the muscularis mucosa is present (Fig. 1) the villi are taller, slimmer, and lie more closely together than when this tethering layer is absent. Without a muscularis mucosa and a measure of mucosal stretching due to too much handling of the biopsy the appearance with broad-based, widely-sep...