The effects of dietary glutamate/glucose Maillard reaction products (MRP) on the rat were studied. Rats fed 5 and 10% MRP developed severe diarrhoea that persisted throughout the 5-wk feeding study. An increase in water consumption by these animals was attributed to excessive faecal water losses due to diarrhoea. Body weights were significantly depressed in animals fed 10% MRP compared with rats fed a control isocaloric diet or a diet containing 10% of an unreacted mixture of glutamate/glucose. MRP ingestion also resulted in a dose-related caecal enlargement, which was accompanied by a decrease in the osmolality of caecal contents, compared with control values. Relative kidney and liver weights were significantly increased in rats fed 10% MRP. Despite a high background incidence of cortico-medullary nephrocalcinosis in all groups in the study reported here, the condition was significantly more pronounced in rats fed MRP, as assessed by mineral analysis and histological examination. In addition, bladder urothelial thickness was significantly greater in rats fed either level of MRP compared with values for control animals. Finally, caecal goblet cell density was significantly reduced in rats fed MRP compared with counts for control animals.