Investigations dealing with the experimental production of urinary calculi have been reported in previous communications.1In a high proportion of albino rats maintained on a diet deficient in vitamin A, urinary calculi developed. If the deficiency in the diet was continued for a period of 250 days, 85 per cent of the experimental animals exhibited vesical calculi and 42 per cent showed renal calculi. The spherical, light brown calculi varied in size from 0.5 to 8 mm. in diameter. They contained calcium phosphate chiefly, with traces of carbonates and a small amount of mucoid substance. No oxalates or uric acid were detected. METHODS OF PRODUCTION OF URINARY CALCULI Three constant changes were observed in the experimental animals that might be associated with calculous formation. They are (1) keratinization of the epithelium of the genito-urinary tract, (2) urinary infection and (3) alkalinuria. 1. The keratinization of the epithelium is noted