The supreme courts of Arizona in State v. Chapple and of California in People v. McDonald have recently ruled that a trial judge committed reversible error in refusing to admit expert testimony on eyewitness identification. Both courts concluded that the expert testimony would add to the jury's knowledge. They offered several specific criteria for decisions on including expert testimony. Several research studies have showed the problems involved in the jury's task and both the advantages and the limitations of the data underlying expert evidence on eyewitness testimony. The two alternatives often suggested in case law -cross-examination of the witness to uncover inaccuracies or bias and the use of judicial instructions regarding problems in eyewitness identification -- do not offer all the advantages of eyewitness testimony. The continued use of experts by defense attorneys is likely to give rise to their use by the prosecution as rebuttal witnesses. Because of this possibility, defense attorneys should reserve these expert witnesses only for important cases. The current situation is not a balanced one and may cause hesitation in accepting the widespread use of expert witnesses in eyewitness identification cases. 222 footnotes.