The physiologic basis of many varieties of dysfunction of the bladder is as yet ill understood. Patients present themselves with frequency, urgency or difficulty in urinating for which no adequate explanation is found in the urinary tract. Although it is generally recognized that a lesion of the central nervous system, of the peripheral nerve supply or of the musculature of the bladder can produce dysfunction, the actual cause of symptoms in many patients is frequently overlooked. In interpreting these symptoms assistance is obtained by studying the activity of the bladder and the sensations experienced by the patient during filling. By using a cystometer with a constant recording mechanism, a graphic representation of the reaction of the bladder to filling is made, and the points at which sensations are experienced can be plotted on the tracing. However, it is well to keep certain effects in mind in interpreting the curves. It