The article takes a close look at the claim that the Japanese Foreign Ministry's policy of “inseparability of politics and economics” (seikei fukabun) hampered Soviet-Japanese economic relations in the 1980s. Taking three case-studies (South Yakut coal, Sakhalin oil and gas, and the Siberian pipeline), the author shows that the loss of interest on the part of Japanese business circles in investing in the Soviet economy had little to do with the political priorities of the Japanese Foreign Ministry, and much to do with the changing energy needs and structure of the Japanese economy and its shift towards greater resource-efficiency. The article concludes, therefore, that the solution of the “territorial problem” would have hardly contributed to increasing Japanese investment in the Soviet Union; hence seikei fukabun was based on a false premise. The findings may be relevant to the ongoing territorial dispute between Japan and Russia and, in a broader sense, between Japan and its other neighbors, notably China.