A reaction system consisting of (oxygen-consuming) tyrosinase immersed within a perfluorochemical emulsion was investigated by comparing the activity and stability of the enzyme within the emulsion to that within pure buffer. The perfluorochemical emulsion contained 30 v/v% perfluorooctane, 70 v/v% aqueous buffer and pluronic-F68 as a surfactant. The catecholase activity of soluble mushroom tyrosinase was chosen for study and catechol was used as a substrate. A turnover parameter of 0.50 absorbance units and an inactivation rate constant of 0.012 s(-1) were found in the presence of a perfluorochemical emulsion and a turnover parameter of 0.53 absorbance units and an inactivation rate constant of 0.012 s(-1) were found in the absence of perfluorochemicals (pure buffer). The enzyme demonstrated no appreciable loss in performance within the perfluorochemical emulsion relative to its behaviour within aqueous buffer. This implies that the local concentrations of oxygen are the same under both systems and that under conditions when oxygen is limited in an aqueous system, tyrosinase performance would be improved within the perfluorochemical medium.