Renal mineralization is a commonly encountered lesion in old rats and its presence at times complicates the interpretation of data derived from chronic rat studies. The feeding of sucralose, a new and high-intensity sweetener under regulatory review, resulted in caecal enlargement and an increase in the incidences of renal mineralization and pelvic epithelial hyperplasia. These responses prompted a review of the literature focusing on the relationships, if any, between the caecal and renal changes. The literature supports the contention that caecal and renal changes occur frequently in response to feeding poorly absorbed osmotically active substances to rats. Some possible mechanisms that may be involved in the development of the renal lesion are discussed.