A. The administration of histamine was followed by slight improvement both in the clinical picture and Rorschach test for the group, particularly in the characteristic catatonics. From the absence of striking change, one might reflect that while histamine may be able to influence the psychosis in certain cases, cases of long duration and resistant to metrazol were refractory material for eliciting improvement, and cautious administration precluded the effects of a truly profound vascular shock. For future trials, a sharper increase in dosage and even cautious intravenous administration should be considered. Comparison of post-histamine tests with metrazol prognosis studies9 suggests that these patients are somewhat more likely candidates for metrazol improvement than they were before histamine.B. Following histamine, the catatonics showed psychological test changes identical in direction with the changes observed after metrazol. In the depressive cases, the changes differed from those of the catatonics as was also the case with metrazol. Although control series with water injections and without injection were not carried out, the essentially uniform test changes serve to validate the findings. Similarity in psychological response to widely different pharmacodynamic agents without discernible physiological similarity, seems to permit formulation of a therapeutic moment in terms of "nonspecificity." The psychological effects of histamine as of metrazol appear to depend on the personality and illness structure of the patient. The fact that psychological changes following histamine, as shown in the Rorschach test, are in the same direction as those elicited by metrazol and sodium amytal,14 suggests a non-specific action of the drugs on psychoses. This non-specific action might perhaps be explained by the hypothesis that these drugs interfere with the homeostatic equilibrium, which was shown to be rigid in schizophrenia.15 There is no clear reason as yet to consider even the profound disturbances of cerebral oxidation by metrazol or insulin as other than more potent exemplars of this principle.C. The method applied in this experiment is suggested as a means of investigating the psychological effects of drugs capable, on proper application, of a degree of objectivity and quantitative measurement which seems to the authors otherwise unattainable at the present time.Abstract Teaser