The authors describe the development of a preventive program focused on intravenous drug users at risk of HIV infection, using the Social Network Approach as the intervention model. The authors describe the project's steps in a large university hospital in southern Brazil, emphasizing the unique methods and techniques developed by the treatment staff. Problems encountered during the project development are discussed, aimed at identifying the reasons why the program only achieved partial success. The authors identify critical issues, such as the use of a new technique not previously tried in Brazil, difficulties in maintaining IV drug users in treatment, lack of infrastructure for walk-in treatment, and the challenge of motivating staff and patients to continue treatment. The authors conclude by listing suggestions aimed at facilitating the development of new projects based on the same conceptual model.