Political blogs have emerged as a new journalistic format that has gained influence on the political discourse in the United States. Previous research has shown that this influence stems mainly from attention given to blogs by traditional news media. Based on the concepts of intermedia agenda setting and agenda building, this study explored the source interaction between 10 elite traditional news media and 10 political filter blogs during the 2006 Congressional Midterm Elections. An analysis of 2587 sources used in the election context found that traditional news media frequently cited blogs in their election coverage, but that the source attributions to the blogs were vague. Blogs, on the other hand, heavily cited traditional news media, but the analysis revealed that conservative blogs cited elite traditional news media less than did liberal blogs. Conservative blogs relied more on conservative media outlets in their election coverage. A case study of the dominant election topic, the Mark Foley scandal, showed that the daily interaction between the two media formats was driven by the use of breaking news elements as well as controversial opinions. The findings of this study show that the blog agenda is strongly influenced by traditional news media sources and that blogs at the same time have become part of the routine newsgathering process of traditional news media journalists. However, the findings also raise questions about changes in the standard journalistic research and attribution procedures as both media formats often rely on each other as sources rather than on original reporting.