Although there is a substantial research literature on the effects of random responding on the MMPI-2 (Butcher, Dahlstrom, Graham, Tellegen, & Kaemmer, 1989), there are very few studies available on this topic with the MMPI-A (Butcher et al., 1992). Archer and Elkins (1999) found that MMPI-A validity scales F and VRIN were particularly useful in detecting entirely random profiles from those derived standardly in clinical settings but noted that "all random" protocols could not be used to evaluate the usefulness of the T-score difference between the first half (F1) and the second half (F2) of the MMPI-A test booklet. Following up on this issue, this study extended the methodology of previous research by examining the hit rate, positive predictive power, negative predictive power, sensitivity, and specificity of VRIN, F, F1, F2 and the absolute value of the T-score difference between F1 and F2 (denoted as IF1-F21) in 5 samples varying in the degree of protocol randomness. One of the samples consisted of 100 adolescent inpatients administered the MMPI-A under standard instructions, and another sample consisted of 100 protocols randomly generated by computer. The additional 3 samples of 100 protocols each contained varying degrees of computer-generated randomness introduced in the latter half of the MMPI-A item pool. Over- all, the results generally indicate that several MMPI-A validity scales are useful in detecting protocols that are largely random, but all of these validity scales are more limited in detecting partially random responding that involves less than half the total item pool located in the second half of the test booklet. Clinicians should be particularly cautious concerning validity inferences based on the observed T-score difference that occurs for the F1 and F2 subscales and current findings do not support the clinical usefulness of this index.