• Glucuronides increase the solubility of calcium phosphate. Excretion of glucuronides in the urine can be increased by administering compounds, such as the salicylates, that conjugate with glucuronic acid. Acetylsalicylic acid was therefore given orally to a series of patients with frequently recurring calcium-containing calculi. One patient had passed approximately 100 calculi in 14 years, and 12 patients had collectively undergone 23 major operations for removal of calculi. All patients in this series had had a "stone episode" within a year of starting treatment or had renal calculi in situ at the time. In addition to 2 gm. of acetylsalicylic acid, treatment included liberal water and low-calcium intake. It was almost always possible to double the pretreatment urinary output of glucuronides; sometimes it was tripled or quadrupled. Salicylamide proved even better than acetylsalicylic acid and is used in all cases now. In 17 out of 19 patients there was no recurrence of calculi. In one patient there was recurrence, and in another some preexisting calculi increased slightly in size. The therapy prevented the common incrustation of inlying catheters in eight out of nine patients whose catheters previously became obstructed in one or two weeks. Salicylates are recommended for further trial as means for preventing recurrence of calcium-containing urinary calculi.