The Minnesota Multiphasic Personality Inventory--Adolescent (MMPI-A) and Minnesota Multiphasic Personality Inventory--2 (MMPI-2) True Response Inconsistency (TRIN) scales are measures of acquiescence and nonacquiescence included among the standard validity scales on these instruments. The goals of this study were to evaluate the effectiveness of these scales in detecting varying degrees of acquiescence and nonacquiescence and to evaluate cutoff scores for clinical use. After the removal of invalid protocols from the MMPI-2 and MMPI-A normative samples, each normative sample was randomly divided in half. For each measure, one half of the normative sample served as a comparison group and the other half was modified with increasing degrees (10%, 20%, 30%, 40%, and 50%) of randomly inserted true or false responses. The results for a 9.1% base rate of acquiescence or nonacquiescence provide support for TRIN cutoff scores at or near those presented in the MMPI-A and MMPI-2 manuals. (Contains 8 tables.)