This study examines the ethical aspects of designing preventive health strategies in the workplace that rely on biochemical indexes of worker susceptibility. It analyzes the benefits and risks of this type of occupational testing, and stresses the desirability of guidelines for the use of hypersusceptibility testing in preemployment screening. The primary value of using such programs to identify previously unsuspected hazards in working environments is underscored. The report proposes elements for effective guidelines that can permit the orderly development of hypersusceptibility tests. Further study is needed to validate these technologies; to review the legal elements of consent and disclosure requirements; to assure continuation of equal employment opportunity; to provide legally enforceable protections of workers as research subjects; and to identify the extent, if any, of possible social and psychological harms imposed by such testing.