The leading case on the admissibility of scientific expert testimony is Frye v. United States. In Frye, the defendant offered expert testimony on the results of a systolic blood pressure deception test, a test similar to the current lie detector test. The trial court denied admission of the results into evidence, and the defendant appealed. The appeals court concluded that the test was not admissible because it had not gained standing and scientific recognition among physiological and psychological authorities. Federal Rule of Evidence governs the admissibility of expert testimony, and Rule 703 requires courts to examine the reliability of expert sources. Another approach to the admissibility of scientific expert testimony is the balance test which requires that the reliability of the technique used outweigh its prejudicial effect, as stated in Federal Rule of Evidence 403. It is concluded that the Frye rule represents the best approach to scrutinizing and admitting scientific expert testimony. The rule shields courts from unreliable scientific evidence by regarding that a new scientific theory produce a sufficient amount of proof to satisfy experts before it is deemed sufficient to influence the outcome of litigation. 142 footnotes