Professionals with advanced training in natural, physical, social and applied sciences or ``experts'' are important actors in international environmental negotiation. Experts participate in environmental negotiation by identifying problems, building and testing theories, communicating science knowledge and advising. They are generally less prominent in formal bargaining. This paper considers whether environmental negotiation is facilitated when experts participate in the formulation and detailing of agreements. Case material explores the regime of the Baltic Sea where civil servants with advanced training in science and engineering are direct participants in the regime's annual cycle of negotiations. The inquiry begins in 1983 and ends in 1995. During this period, expert-diplomats failed to reach consensus on politically-binding recommendations bearing on the region's most pollution-prone industry, the pulp and paper industry. Conditions for consensual decision-making were present: member states' expert-diplomats were individuals with similar technical training, professional values, and responsibilities. Yet conflict prevailed over consensus, driven by experts' narrowly defined research agendas and their allegiances to particular problem-solving technologies. These differences were magnified by the negotiators' pride in national scientific and technological institutions and capabilities.