Vote mobilization qua local and national organizations has played an important role in postwar Japanese elections for both Houses of Parliament. However, while there is an abundant literature on personal support organizations (kôenkai) of individual politicians in the Lower House, the role of national organizations for vote mobilization in Upper House elections has so far received only scant attention. The phenomenon of the ‘organized vote’ in postwar Upper House elections in Japan raises a number of questions. How important has it been in terms of voting behavior? What are the factors underlying organized voting? And how has the electoral clout of national organizations changed over time? This article tries to make a modest contribution to the debate on ‘organized voting’. In particular, it addresses the proposition that the ability of national interest groups to mobilize votes has declined significantly. The main empirical point of reference in this article are the 2001 Upper House elections.