This work investigated the stability of commercial horseradish peroxidase in compressed carbon dioxide and propane. Effects of temperature, exposure time and pressure on the enzyme activity were evaluated. The results obtained indicated that the HRP treatment in CO2 promotes a significant decrease in the enzyme activity. whereas HRP showed good stability in propane, indicating that this enzyme is more stable in propane than in CO2. Far UV-circular dichroism (CD) analyses of HRP in solution indicated that treatment of the enzyme with propane did not induce changes in the secondary structure content of HRP. On the other hand, incubation with CO2 led to significant loss of HRP secondary structure. The solid HRP did not present decrease of its activity after treatment with pressurized CO2 or propane. The CD analysis of solid HRP treated with propane and CO2 revealed that the enzyme once more present higher stability in propane, but the treatment in both solvents provoked loss in secondary structure. (C) 2009 Elsevier B.V. All rights reserved.