Practitioners have frequent contact with populations underrepresented in scientific research--ethnic/racial groups, sexual minorities and others at risk for poor health and whose low participation in research does not reflect their representation in the general population. Practitioners aspire to partner with researchers to conduct research that benefits underrepresented groups. However, practitioners are often overlooked as a work force that can help erase inclusion disparities. We recruited (n = 282) practitioners (e.g. physicians, social workers, health educators) to examine associations between their attitudes toward research purposes, risks, benefits and confidentiality and their involvement in recruitment, interviewing and intervention facilitation. Participants worked in community-based agencies in Madrid and New York City (NYC), two large and densely populated cities. We used cross-sectional data and two-sample tests to compare attitudes toward research and practitioner involvement in recruiting, interviewing and facilitating interventions. We fit logistic regression models to assess associations between practitioner attitudes toward ethical practices and recruitment, interviewing and facilitating interventions. The likelihood of recruiting, interviewing and facilitating was more pronounced among practitioners agreeing more strongly with ethical research practices. Though Madrid practitioners reported stronger agreement with ethical research practices, NYC practitioners were more involved in recruiting, interviewing and facilitating interventions. Practitioners can be trained to improve attitudes toward ethical practices and increase inclusion of underrepresented populations in research. Funders and researchers are encouraged to offer opportunities for practitioner involvement by supporting research infrastructure development in local agencies. Practices that promise to facilitate inclusion herein may be used in other countries.