The concept of diagnostic utility was used to create questions that would differentially affect deception detection accuracy. Six deception detection studies show that subtle differences in questioning produced accuracy rates that were predictably, substantially, and reliably above and below chance. The first 3 detection studies demonstrate that diagnostically useful questioning can reliably achieve accuracy rates over 70% with student and experienced judges. The fourth and fifth experiments demonstrated negative diagnostic utility among federal investigators but not students. The final experiment crossed 3 sets of interview questions with experience. Strong question effects produced a swing in accuracy from 32 to 73%. A questioning by experience interaction was also obtained.