The effectiveness of these instructions was measured in the context of a videotaped trial. Jurors watched an assault trial where the central issue was the identification of the defendant by an eyewitness. One-third of the jurors heard the Telfaire instructions at the end of trial; one-third heard the revised instructions, and one-third had no instruction on eyewitness reliability. Compared to jurors with the Telfaire instruction, those who had the revised instruction were more knowledgeable of the factors to consider when listening to eyewitness testimony. These jurors were also less likely to convict the defendant, even when the identification seemed reliable. Finally, a sample of superior court judges was asked to comment on the Telfaire and revised instructions. They thought the simplified instruction was more effective than the Telfaire instruction at conveying the intended legal concepts to the jury, but also rated the revised instruction as more strongly biased toward the defense. Tabular data, a 31-item bibliography, and appended texts of the instructions are provided. (Author abstract modified)