The stimulus behind this investigation was created by various factors which can only be enumerated briefly. In the course of routine sero-diagnosis of syphilis in psychiatric work at the Institute during the last five years, it became evident that, of the three flocculation tests employed, the Kahn (Kahn, R. L., 1928), Müller-Ballungs reaction (Müller, R., 1929), and Meinicke Klarungs reaction (Meinicke, E., 1929), the Meinicke original extract gave results superior in sensitivity. This feature was shown particularly in very early infections and treated cases. Three Wassermann tests, the standard method for psychiatry (Mann, S. A., and Partner, F., 1931), the Wyler drop technique (Wyler, E. J., 1929), and the Browning and Kennaway methods (Browning, C. H., and Kennaway, 1924), run concurrently, could not claim to be as good in this respect, and further, were liable to give non-specific results. The explanation of some of the anomalous reactions of one or another of the three hæmolytic systems seems to lie chiefly in the fact that sera from psychotic and mentally defective patients contain in larger degree elements that are prone to disturb specificity.