Measurements of bladder pressure have been made from time to time for experimental purposes, but no successful attempt has been made to apply such observations in a convenient way to ordinary diagnosis. It is probable also that not even their importance in clinical diagnosis has been realized. The present paper, however, will attempt to show that such measurements are of great value in diagnosis and that, by means of a specially devised instrument, they can be made easily and with sufficient accuracy to afford much important clinical information. It is felt, furthermore, that a new principle in diagnosis has hereby been added. Starting with the well known anatomic fact that the bladder wall and its internal sphincter are chiefly in control of the sympathetics and parasympathetics, I believe that measurements of intracystic pressure, with known quantities of fluid, might throw much light, not only on the question of whether or