Data for this study were derived from participant observation of 918 grand jury cases from November 1971 to February 1972, indepth interviews with former members of Harris County grand juries, and 271 questionnaires mailed to all persons who served on Harris County grand juries between 1969 and 1972. Because Harris County is located in a State that is both southern and western and has a sizable minority population with a large influx of persons from the east and midwest, it is reasonable to suggest that Harris County is representative of modern American society. Although the upper socioeconomic representation of the grand jury apparently contributes to jurors' concern with the rights of the accused, the grand jury does not fulfill its ideal function of carefully screening and evaluating the prosecutor's evidence to determine probable cause that a crime was committed. One reason for this is inadequate training for newly selected grand jurors. This makes the jurors vulnerable to becoming 'rubber stamps' for the district attorney's staff. Moreover, evidence indicates that the district attorneys do take advantage of ignorant grand juries by withholding significant information from grand jury purview and by deliberately routing to the grand jury cases for which they expect to receive favorable grand jury decisions. The heavy volume of grand jury cases also renders a fair hearing unlikely. The small percentage of cases receiving careful analysis by the grand jury tends to consist of the more bizarre, infamous, or salacious cases, reflecting the preoccupation of the upper middle class. Forty-six footnotes are listed. (Author summary modified)