The overall goals of this project are to determine whether (a) a special orthophosphate preparation (slow-release potassium phosphate or UroPhos-K) would produce physiological-physicochemical correction, inhibit stone formation, and provide safety of usage in absorptive hypercalciuria, and (b) a novel citrate formulation (potassium-magnesium citrate or K-Mag) would inhibit stone formation and provide safety of usage in patients with calcium stones. In Aim 1, we shall examine the effect of UroPhos-K on the crystallization of stone-forming salts while patients are kept on a constant metabolic diet. Aim 2, to commense upon satisfactory completion of Aim 1, will be a long-term randomized trial between UroPhos-K and placebo on stone formation. In Aim 3, we shall continue ongoing randomized trial between K-Mag and placebo on stone formation. Finally, Aim 4 will assess the value of K-Mag in preventing hypokalemia and magnesium depletion in patients taking thiazide for hypercalciuric nephrolithiasis. This project is biomedically important, since it could lead to the development of UroPhos-K as a rational and effective treatment of absorptive hypercalciuria, and of K-Mag as a superior drug over potassium citrate.