Increased use of mental tests for the study of psychoses and allied disorders is conspicuous in recent psychiatric practice. This increase is most prominent first in the use of Rorschach's ink-blots; second, in the investigation of conceptual thinking with methods originated by Goldstein; third, in the study of psychometric pattern; fourth, in the diagnosis and measurement of intellectual deterioration; fifth, in assessing prognosis and the effects of treatment. It is partially attributable to sharpening of interest, due to the war, in the prediction of break-down under stress, in the stability and social potentialities of border-line groups, and in estimating the effects of head injury. Another factor is that popular modern treatments such as shock therapy and prefrontal leucotomy appear to involve cerebral areas intimately associated with intelligence. The greatest advances, however, have been made by the followers of Rorschach and of Goldstein and their contributions began before these factors arose. Their methods are also much applied in investigations under the fourth and fifth headings. Their influence, too, is discernible in a change now developing in the way of using mental tests. Whereas in most early investigations tests were used quantitatively as instruments for studying how intelligence level affects and is affected by psychosis, the modern tendency is to use tests not as measuring instruments, but as standard interviews or situations in which the quality rather than the level of the subject's behaviour is studied. On the other hand, perhaps it was growing recognition of the unsuitability of most quantitative tests for application to adults, and of the additional difficulties of interpreting results in psychoses, that first induced search for other techniques.