A domestic ratification game nested within an international bargaining game establishes that domestic politics influences the outcome of international negotiations. When information on the domestic side is incomplete, an informational role of lobbies is established. Cooperation is more likely when domestic lobbies provide information to Congress about a treaty presented for ratification, especially when cooperation would not otherwise occur. As government becomes more divided, cooperation is less likely; when it does occur, the legislature is better off - internal divisions worsen the external leverage of states, while a united home front is the executive's best chance for obtaining her ideal agreement. Copyright 1996 Blackwell Publishers Ltd..