The effectiveness of the MCMI-III Validity scale, Scale X, and the Clinical Personality Pattern scales to detect random responding is put to the test. The binomial expansion and Monte Carlo techniques were used. If the examiner is willing to interpret tests of questionable validity, then 50% of the random responders will not be detected. Scale X and the Clinical Personality Pattern scales were useless in detecting random responders. © 2002 Wiley Periodicals, Inc. J Clin Psychol 58: 1615–1617, 2002.