Study data came from 67 adult men and women living in Santa Cruz County (Calif.). The subjects were randomly assigned to one of two conditions in which they were exposed to standard criminal voir dire that either included death qualification or did not. Subjects who were exposed to death qualification were significantly more conviction-prone, more likely to believe that other trial participants thought the defendant was guilty, more likely to sentence the defendant to death, and more certain that the law disapproves of death penalty opposition than were subjects who did not undergo the death-qualification process. Several psychological features of the death qualification process may account for the biasing effects. Persons placed in novel or unfamiliar situations are especially sensitive to cues from authority figures and from apparently knowledgeable others, such as judges and attorneys in the courtroom. By requiring the attorneys and judges to dwell on the issue of penalties at the very start of the trial, the death qualification process implies a belief in the guilt of the defendant on the part of these major trial participants. Death qualification also requires jurors to reflect upon the necessity of their deciding between the life and death of the defendant. Research suggests that thinking about or imagining an event increases an individual's estimate that it will occur. Footnotes, tables, and a list of 14 references are included. (Author abstract modified)