The weight, the total crypt cell population, and the proliferation parameters of the colon were estimated in rats during a 4-week administration of a liquid elemental diet (Vivonex standard). Both mitotic and DNA synthesis activity were decreased (P less than 0.01) in the colonic mucosa during the administration of the diet. The weight of the colon was electively decreased (P less than 0.01) from the first week of the treatment. After four weeks, a 75% decrease in the cell population of mucosal glands was observed. This showed that considerable atrophy of the colonic mucosa occurred under the effect of feeding the elemental diet. This atrophy was probably mediated by a reduction in the proliferative activity of the stem cells in the mucosal glands.