Three domains related to drug use included: aspects of the older brother's personality, the relationship existing between the brothers, and the personality of the younger sibling. Since previous research has been limited, this study employed a "risk/protective" mechanism to examine the ways older brothers can serve as buffers to offset risk-taking behavior in younger brothers. The participants answered questionnaire items which were based on intercorrelations and reliabilities and were adapted from previous scales. According to the "Personality Influence Mechanism," the younger brother can be influenced by the older brother through identification. "Genetic Temperament Connection" highlights genetic factors that explained similarities in sibling behavior. "Environmental Reactive Mechanism" focused on troubled relationships between the brothers relating to inner conflict and intrapsychic distress in the younger sibling which, in turn, can cause unconventional and irresponsible behavior in the latter. 6 tables and 31 references