Noninjecting heroin use (NIU) is spreading among social networks of young Mexican American polydrug users. This article examines the influence of family and peer networks on NIU behavior and other drug practices and risks. This study delineates the extent to which a culturally relevant modification of the "network facilitation" theoretical approach can increase both a theoretical and practical understanding of drug use and related risk behaviors. Using the methods of analytic ethnography, it identifies, describes, and explains variations in the social networks among this marginalized population and how specific aspects of Mexican American culture (familismo, and collectivismo) affects risk behaviors.