Two experiments tested a new computer-based lie-detection technique. The Timed Antagonistic Response Alethiometer (TARA) manufacturers a situation in which, if respondents lie, they must perform two incompatible tasks, whereas if they tell the truth, they can perform two compatible ones. Both tasks involve repeatedly classifying target and control statements as true or false. The incompatible task combination, being more difficult, takes longer to complete correctly; hence, slower responses diagnose dishonesty. Experiment 1 found that, while concurrently classifying control statements honestly, participants invariably took longer to classify target statements dishonestly than honestly. Exploiting this effect, Experiment 2 found that separate groups of liars and truth-tellers could be distinguished with about 85% accuracy. The properties and potential of the technique are discussed. Copyright © 2006 John Wiley & Sons, Ltd.