General constitutional concerns of the court structured the examination of scientific evidence on appeal in the Birmingham Six case in 1987-1988 and 1991. The court's concern to uphold the primacy of the jury and its own legal procedures led it to subject scientific witnesses to cross- examination and require appellants to disprove conclusions presumed to have been reached by the jury. Cross-examination was not used as scientists expected, to see if the original scientific evidence met current scientific standards, but rather to see if presumed conclusions of the original jury should be altered. Methods and objectives adopted by the court allowed it to construct judgments that discredited the standards used by prosecution scientists at the original trial but that recognized the conclusions reached. Divergence between scientific analysis of prosecution evidence and that undertaken by the Court of Appeal showed up in the process of cross-examination; scientists were asked to offer convincing answers to questions not posed before. In the Birmingham Six case, the presence of new scientific evidence seemed to make a crucial difference. This new evidence provided the Court of Appeal with an alternative explanation for earlier positive results but under abnormal circumstances. The authors conclude that miscarriages of justice may be inevitable and discuss the basis for challenging scientific evidence on appeal and the jury's treatment of scientific evidence. A historical review of the British system of criminal appeals is presented. 29 references and 7 notes