Renal dysfunction is so commonly present in cases of mental breakdown that it is of interest to know whether it is especially associated with any definite clinical type or types of mental disorder. In an endeavour to ascertain this, cases have been selected from recent admissions in which the form of disorder from a clinical point of view appeared to be sufficiently marked to warrant placing them in a definite category. Many cases present such a mixture of cycloid, schizoid, confusional or paranoid indications that in an investigation of this nature the selection of sufficiently clear-cut types from a clinical standpoint is not altogether an easy matter. To determine the degree of concentration and polyuria, Rosenberg's modification of the Volhard test has been adopted. It involves little discomfort to the patient and is as follows:—