Struvite crystals were previously shown to form primarily as a result of urease-induced alkalinity and supersaturation. In vitro perfusion of struvite crystals with undersaturated urine caused crystal dissolution. Complete dissolution of human struvite urinary stones was demonstrated during 6 wk of perfusion in vitro with undersaturated human urine. Human hydroxyapatite stones perfused similarly underwent only slight dissolution. A glycoprotein precipitated as the stones dissolved; the pathogenic significance of the glycoprotein is unknown.