Undergraduates (63 men. 68 women) were administered the Minnesota Multiphasic Personality Inventory (MMPI) and MMPI-2 in counterbalanced order, 1 week apart, to examine invalid response sets in the MMPI versus the MMPI-2, in research volunteers. A number of participants had clinically significant elevations on Infrequency (F) and Back F (Fb). Examination of Variable Response Inconsistency (VRIN), True Response inconsistency (TRIN), and the new Infrequency-Psychopathology [F(p)] scale suggested elevations were due to endorsing highly infrequent items rather than random responding or psychopathology. When the profiles were rated for goodness-of-fit to six modal-invalid profile types, a number of profiles were possibly invalid. Gender differences were observed but few differences between the MMPI and MMPI-2 were found. However, the additional MMPI-2 validity scales and the F(p) scale improve detection of invalid response sets. Demographic and motivational factors, and recommendations for obtaining valid results from undergraduate volunteers, are discussed.