The heat flow reaction calorimetry technique was developed for reactions with supercritical fluids and was applied to monitor the free-radical dispersion polymerization of methyl methacrylate in supercritical carbon dioxide (scCO(2)). The main mathematical equation for the calorimetric calculations was modified to take into account the particularities linked to the supercritical nature of the solvent. As a result, important heat transfer variables, such as the overall heat transfer coefficient, can be measured at the actual reaction conditions. This information is later used to calculate the heat released by the reaction and thus monitor its evolution. The robustness and accuracy of the technique allowed also investigating the effects of several reaction parameters. Finally, the obtained data were used to illustrate the importance of pressure as far as the safety of the reaction is concerned.