An analysis of significant judicial decisions finds that since 1968 judges have used empirical social science data to consider the issue of the neutrality of death-qualified juries. Using 811 eligible jurors another study concludes that the practice of death qualification in captial cases excludes a large group of potential jurors, threatens the representativeness of the jury, and results in a group of jurors who have different attitudes about crime control and due process than do those who were excluded. Findings of a study in which 288 subjects watched a videotape of a simulated homicide trial reveals that death-qualified jurors are more likely to convict a defendant than are excludable jurors. A study of death qualification and its effect in the insanity defense concludes that the process of death qualification of a jury undermines the insanity defense, which is one of the most important defenses available to the mentally ill. Two studies of the behavior of potential jurors find that both the differing interpretations of evidence and the differing thresholds of conviction may mediate the relationship between jurors' attitudes toward the death penalty and their verdicts. An analysis of persons who would always vote for the death penalty shows that the exclusion of these people from juries in capital cases would have a negligible impact. Further studies demonstrate that the process used in death qualification has a biasing effect which is independent of its effect on the composition of the jury. Footnotes, data tables, and reference lists are included for the studies.