The implication of intraluminal hyperpressure in the pathogenesis of colonic diverticulosis was investigated. Since colonic motricity depends on the anatomical integrity of the myenteric plexuses, we looked for morphological abnormalities of these plexuses in diverticulosis of the sigmoid, using the silver impregnation technique devised by Smith. Fifteen sigmoidectomy specimens (including the rectosigmoid junction) were studied in patients afflicted with diverticulosis. Operations were not performed during the acute phases of the illness. The results were compared to those obtained in 5 colectomy specimens in patients with cancer of the rectum, without colonic diverticulosis (control series). Conventional histology as well as the silver impregnation did not reveal any morphological abnormalities of the myenteric plexuses in the rectosigmoid junction or in the remaining sigmoid. The count of argyrophilic ganglion cells (10 to 15 per plexus) was identical in the colons affected with diverticulosis and in the control specimens. These results show that impairment of motricity in sigmoid diverticulosis is not a consequence of morphological abnormalities of the myenteric plexuses. They do not, however, exclude chemical or functional modifications in these plexuses.