Combining an intuitive approach with crystallization chemistry principles, one would ask the following questions with respect to renal lithiasis: 1) What Starts crystallization in urine? - Nucleation, 2) How much can precipitate? - Supersaturation level, 3) How fast can the precipitate form? - Crystallization rate, 4) What form does the precipitate have? - Habit, Aggregation, 5) What accounts for retention of the precipitates (stones) in the kidney? - Size, Aggregation, Adhesion to cell membranes. With the perfection of our techniques for quantitating the metastable limits (MSL), supersaturation levels (SSL) and crystallization rates (CxR), we are now in a position to: 1) evaluate the role of macromolecular weight components (glycoprotein fractions, proteins, amino acids, polysaccarides,.) and small molecular weight components (citrate, Na plus, Cl minus, SO equals Mg ions,.) of natural urine on the MSL, SSL, CxR of calcium oxalate, and 2) evaluation and monitoring of antistone therapy on the MSL, SSL, and CxR of human urine with respect to calcium oxalate. Specifically with respect to Urinary Macromolecules (MM) we propose further studies under the following headings: I) Crystal Chemistry,II) Biochemistry (Fractionization and Characterization of Urinary MM) III) Production of Urinary Macromolecules, IV) Other Crystal systems, V) Urinary Macromolecules vs. Urinary Micromolecules. BIBLIOGRAPHIC REFERENCES: Evaluation of Renal Masses Including Retrograde Renal Brushing. Gill, W.B., Bibbo, M., Thomsen, Sharon, and Lu, C.T. Surgical Clinics of North America, Vol. 56: No. 1, February, 1976, p. 149-173. Circle Tube Nephroureterostomy: Additional Experience with an Alternative Method of Urinary Diversion, Borden, T.A., Gill, W.B., and Lyon, E.S. Surgery, Gynecology, and Obstetrics, 140: 547, 1975.