AbstractPrevious attempts to differentiate brain‐damaged from schizophrenic patients largely have been inconsistent when employing various methods derived from the MMPI. Russell developed an MMPI key for this purpose that is based on an explicit rationale of differential MMPI test performance for these populations. The present study used this MMPI key in an attempt to distinguish 20 brain‐damaged, 21 schizophrenic and 24 clinically depressedSs. The results demonstrated that the key has some clinical utility in making the distinction between brain damage and schizophrenia; however, it performed poorly in correctly classifying the depressed