Full-scale comparison of Negro and white mental patients is not possible today because the federal statistics take no account of race. Earlier studies of limited populations were partially vitiated by racist interpretations or by limited samples. Malzberg's study of over 20 years ago is still our most accurate basis of comparison; there is need for a replication of this study today for an analysis of changing trends. Wartime researches have shown results similar to those of Malzberg, but they lack systematic character.There are pitfalls in accepting many of these comparative studies at face value; to avoid these difficulties it is shown that their incorporation of certain common assumptions makes their interpretation questionable without proper sociological analysis. Where 2 racial populations are compared in terms of social variables, it is relevant to note 3 major assumptions: (1) That Negro and white populations may be considered essentially alike except for the variables in question; (2) that the experiential meaning of these variables is culturally equivalent in both groups; and (3) that consideration of each variable by itself, rather than a specially organized cluster of variables as a unique constellation may be the relevant factor. Illustrations of the uniqueness of the Negro's social environment are given to clarify the theoretical issues.In conclusion it is noted that inadequate appreciation of the sociological dimensions in the differential racial environments may lead the researcher or clinician to overlook variations in the development of the personality with consequent difficulties in assessing etiological factors, accurate diagnosis, or therapeutic proceedings.