Jejunal biopsy specimens from nine Spanish children with gluten-sensitive enteropathy were studied with morphometric and immunohistochemical techniques in three stages of the diseases: the first biopsy was taken for diagnosis, when the child had a gluten-containing diet, the second after gluten withdrawal, and the third biopsy after gluten-provocation. The findings were compared with those in 10 healthy adults. The villous:crypt ratio and the length of the surface epithelium per stretched millimetre muscularis mucosae were decreased, whereas the number of interepithelial lymphocytes per millimetre surface epithelium was increased when the child had a gluten-containing diet. Although these parameters improved after withdrawal of gluten for at least seven months, they never reached the values of the healthy control group. With the indirect immunoperoxidase technique it was shown that the numbers of IgA-, IgG-, and IgM-containing cells, expressed per "mucosal tissue unit" of 4 micrometer thick and 1 mm wide, were significantly increased during the active phases of the disease. This increase was most striking for the IgM-containing cells. The most sensitive parameters for the histological diagnosis of gluten-sensitive enteropathy are the villous:crypt ratio or the length of the surface epithelium per millimetre muscularis mucosae, the number of interepithelial lymphocytes per millimetre surface epithelium, and the number of IgM-containing cells per millimetre muscularis mucosae.