Computerized Adaptive Testing (CAT) continues to gain momentum as the accepted testing modality for a growing number of certification, licensure, education, government and human resource applications. However, the developers of these tests have for the most part failed to adequately explore the impact of individual differences such as test anxiety on the adaptive testing process. It is widely accepted that non-cognitive individual differences variables interact with the assessment of ability when using written examinations. Logic would dictate that individual differences variables would equally affect CAT. Two studies were used to explore this premise. In the first study, 507 examinees were given a test anxiety survey prior to taking a high stakes certification exam using CAT or using a written format. All examinees had already completed their course of study, and the examination would be their last hurdle prior to being awarded certification. High test anxious examinees performed worse than their low anxious counterparts on both testing formats. The second study replicated the finding that anxiety depresses performance in CAT. It also addressed the differential effect of anxiety on within test performance. Examinees were candidates taking their final certification examination following a four year college program. Ability measures were calculated for each successive part of the test for 923 subjects. Within subject performance varied depending upon test position. High anxious examinees performed poorly at all points in the test, while low and medium anxious examinee performance peaked in the middle of the test. If test anxiety and performance measures were actually the same trait, then low anxious individuals should have performed equally well throughout the test. The observed interaction of test anxiety and time on task serves as strong evidence that test anxiety has motivationally mediated as well as cognitively mediated effects. The results of the studies are di (PsycINFO Database Record (c) 2003 APA, all rights reserved).