This study examines the role of science in the operation of environmental regimes using the Barcelona Convention/Mediterranean Action Plan (MAP) as a case study. The ‘epistemic communities’ theory suggests that emergence of the Mediterranean Action Plan was largely driven by scientific experts. In order to test the hypothesis that this theory also explains the operation of the regime, we used three methods of analysis. Firstly, we attempted statistical analysis of environmental data available from MED POL, secondly we analysed policy documents prepared by MAP including meeting documents and scientific publications and finally we conducted interviews with scientists. We found that the scientific epistemic community theory is appropriate to explain the formation of MAP, but it cannot account for its current operation.