In this paper, reports of earlier attempts to rate ego functions are reviewed, and a detailed account of a current selection of 12 ego functions from the psychoanalytic literature is presented. Component factors of each function are delineated and examples are provided of how these functions are measured from clinical interview material, psychological test responses and psychological laboratory procedures. A study is then described in which ego function ratings from interviews of matched groups of 25 schizophrenics, 19 neurotics and 21 normals are compared. Differences among groups in the adequacy of ego functioning as measured by rating scales are statistically significant and in the predicted direction, with schizophrenics lowest, neurotics next and normals highest. Agreement among raters independently judging the same material is substantial. The interrelationship among ego functions is discussed and results of a preliminary factor analysis are presented in which four strongly related factors are tentatively identified. Two ego function profiles of individual subjects are also included.