Abstract During the course of this investigation we have encountered two "fakes," both of which were represented by the patients to their respective physicians as having been "passed." They showed less than 2 per cent loss on ignition and proved to be calcium-iron-aluminum silicate rocks. We have also had about a dozen prostatic calculi which were analysed by the "ashing" method. This type of calculus consists of either a mixture of magnesium ammonium phosphate and calcium phosphate, or a mixture of calcium carbonate and calcium phosphate. The above-mentioned stones are, of course, not included in this picture. We hope that this survey and the simple method of analysis presented in these two articles will stimulate further work along this line in various parts of the country. The best similar survey we have seen is that of Leonard and Butt (1) on the types of calculi found in the Pensacola, Florida, area.