The investigators propose to develop and test the feasibility and promise of a combined HIV adherence assessment and intervention application for rural drug users using an available, familiar technology whose reach will grow exponentially: text messaging via mobile phones. By 2007, 84% of U.S. residents had mobile phones, with near 100% mobile phone penetration projected by 2013. While technology adoption is often slower in under-served communities, the trend is different with mobile phone technology. African-Americans are using more mobile phone minutes per capita and increasing their use at a higher rate compared with other ethnic groups. This technology has great potential to reduce health disparities. In this project, the investigators will develop and test the feasibility and promise of a text messaging application and system using Ecological Momentary Assessment methods to detect nonadherence and drug use and immediately intervene to improve HIV treatment adherence in drug users living with HIV/AIDS who reside outside major metropolitan areas. This R34 is a Stage 1b/2a project in the Stage Model of Behavioral Therapy Development that will develop novel interventions and methods, and generate preliminary estimates of effect sizes that will determine whether a larger clinical trial with extended follow-up and cost-effectiveness evaluation is warranted.