The study examined heroin use and dealing among Mexican-Americans in San Antonio, TX. The research evolved from a study of gang violence among Mexican-American gangs in South Texas, which sought to identify and distinguish the relationship between gang violence and drug use among male gangs. Study methods included ethnographic field observations, focus groups, and life history/intensive interviews with 160 male gang members. The study addressed areas of the city with the highest concentration of delinquent behavior and Mexican-American gang activity as well as underclass characteristics. The study showed how a Mexican-American adult prison gang had dominated the heroin market and other street-based drug sellers and dealers such as youth gangs. A major consequence of this circumstance has been the increasing use of heroin among Mexican-American gang members and the transformation of many of these gangs from autonomous youth gangs to extensions of the adult prison gangs. This has been most likely to occur in specific areas identified by adult prison gangs as their territories, notably around public housing projects where recently released offenders are living. A few juvenile gangs were able to maintain their autonomy either by not selling heroin or by resisting through violence. Based on these findings, the researchers concur with gang researchers who have argued that juvenile gangs have a "negligible role" in drug distributions. 49 references