After reviewing some of the literature on specific ego functions, the authors select twelve of them. They define these ego functions carefully and, setting up criteria for evaluation, attempt to measure them in a study of matched groups of schizophrenics, neurotics, and normals. The evaluation is done in the context of whether each subject was operating on his usual psychological plane, or whether he was under the stress of some catastrophic life situation. Material was obtained from three sources: 1, clinical interviews; 2, a clinical psychological test battery; and 3, experimental procedures from the psychological laboratory. Differences among the groups were found to be statistically significant, with schizophrenics lowest, neurotics next, and normals highest.