The growth of calcium oxalate crystals in aqueous solution, normal urine, and urine from stone formers will be studied. The effects of various additives on growth in these media will be examined. Special attention will be focused on the structure and state of hydration of the crystals, since we have found these factors to be important in the growth behavior. The charge on the crystal surface in different media and in the presence of different additives will be measured in an electrophoresis cell.