This thesis main goal is to examine the performance of government agencies and interest groups in the formation of official position in the Brazilian Meeting of the Parties to the Cartagena Protocol. So, what follows is an attempt to examine the extent to which the domestic environment influenced the brazilian negotiators to adopt different positions in the Meetings of the Parties to the Cartagena Protocol. It is argued that the performance in the Brazilian Meetings of the Parties to the Cartagena Protocol can be explained considering the influence of domestic structures, which filters the preferences of organizations representing various segments of society on the issue of biosafety of transgenic. It so happens that ties between the government bureaucracy and civil society organizations formed are unevenly at different times, contributing to that Brazil provide differentiated positions in these meetings. Recent studies in theoretical literature of international relations have emphasized the importance of considering the process of forming the country’s position regarding the level of credibility and bargaining power of the representatives under negotiator. Thus, using the theoretical and conceptual approach known as the Two-Level Games, which discusses the interaction between the levels of domestic and external review. Therefore, it was found that the domestic structures – with primacy of the executive – that contributed to the preferences of the group negotiator (MRE/Itamaraty, MCT and MAPA), influenced the formulation of the Brazilian position at COP / MOP 1 and 2. What we see is that the homogeneous setting of the domestic political arena at that time, embodied by the isolation of the government bureaucracy, influence the profile of the positions taken by Brazil in these two meetings of the Protocol. Already at COP / MOP 3, despite the fact that the domestic structure was more heterogeneous and divided, the negotiating group on that occasion showed the least bargaining power in negotiations to table (level I), to the extent that Brazil has made concessions on the rules for the identification of shipments of transgenics – the coexistence of “may contain” and “contains” runs until 2012 – and contributes with proposals to create a consensus on the establishment of a clear identification for the transboundary movement of transgenics. At the time, the win-set of the domestic political arena proved to be greater at this meeting for two previous, signaling a greater chance of achieving the international agreement. However, emphasizes that this condition has caused the decreased ability to bargain from the government vis-à-vis other negotiators, as foreseen in the argument of the Two Levels Games.