Four per cent of the sucrose component of a cariogenic diet of the 580 type was replaced by a combination of Na2HPO4 + NaH2PO4 + KH2PO4 (mole ratios 4.65/0.52/1.00, respectively) or with NaHCO3 + KH2PO4 (mole ratio 9.82/1). The same combinations were also used to replace 4% of the sucrose component of the modified diet of the 2000 type. Osborne-Mendel rats were fed the former experimental and control diets and Sprague-Dawley rats the latter, for 60 days in each case. The alkali phosphate combination reduced caries more effectively than the bicarbonate-phosphate supplement. However, the former combination increased the formation of the dental calculus more than the latter. The alkali phosphate addition caused formation of renal calculi, especially in the former experiment, whilst no renal calcification was found in association with the bicarbonate-phosphate addition.