The problem of the classification of what are generally designated the paranoid states of schizophrenia has been discussed. In a brief historical sketch some theories regarding the nature of the schizophrenic and paranoid ps ychoseshay.e been reviewed, and some of the more outstanding landmarks in the evolution of our understanding of them has been dealt with. In particular, reference has been made to the work of Kraepelin, Bieuler,and Meyer and the more recent contri- butions of Mapother, White, Macfie Campbell, and Henderson and Gillespie . The division of this material into the schizophrenic and paranoid reaction types following the psychobiological approach has been considered the soundest and the most practical basis for the differentiation of cases and for a clearer understanding of their nature. By comparing and contrasting these reaction types, from the point of view of personality, reactive tendencies, psychopathology, symptoms and course, important differ- ences are brought out in the light of which the case material is examined and reassessed. The problem resolved itself into deciding to which of these reaction types i.he paranoid states most closely approximate. The relation of these states to the affective psychoses has been examined, and their response to physical methods of treatment, as shown by current literature, considered CONCLUSIONS: (1) Paranoid states are more closely allied to the paranoid reaction type than to the schizophrenic reaction type for the following reasons:- - (a) The pre -psychotic personality is rather differ- ent from the schizoid type and approximates more closely to the paranoid makeup, with fre- quent appearance of latent homosexual trends. (b) The social adaptability, as indicated by the school and work record and general adjustment, indicates a degree of maturity and personality integration seldom found in pre -schizophrenic states. (c) The age of onset is usually later than in the schizophrenic reaction type. (d) The clinical picture is introduced by paranoid delusions which continue dominant throughout its course in contrast to the schizophrenic reaction type, where delusions are secondarily determined by affective delapidation. (e) There is little to indicate personality disintegration and mental deterioration after illnesses of several years,of the kind that is seen in the schizophrenic reaction type after illnesses of two or three years and often very much earlier. (f) A common constellation of reactive tendencies whose pattern is predominantly paranoid can be traced throughout the life histories and psychotic developments. (2) Confirmation of the contention that paranoid states involve a different process from schizophrenia is obtained by a reference to the literature in regard to the newer physical methods of treatment in such conditions . There it is found that with insulin, electric convulsions, and prefrontal leucotomy the best results are claimed in the paranoid states. (3) The association of paranoid and affective disorders is here demonstrated, and it is tentatively suggested that this association may be stronger than has been generally realised. This relationship may in part determine the more favourable response to physical therapy so frequently found in paranoid states.