The inactivation kinetics of horseradish peroxidase were determined at several values of pH (3, 4, 7, 9 and 10), temperature (40 to 70 degrees C) and pressure (7, 8 and 9 kbar). The data were obtained by taking samples from the moment that pressure inside the hydrostatic high pressure vessels reached the value specified, and therefore relate to isothermal and isobaric conditions. The inactivation kinetics were non-log linear and could be individually well described by the conventional two-fraction model, but the overall consistency of the kinetic parameters of this model was poor and the model was clearly not robust. Inversely, the kinetic model based on the Weibull probability distribution function yielded good individual fits and also a good overall consistency of the kinetic parameters. The whole set of 327 data points could be well described by an overall model considering that the shape parameter (beta) varied with pressure but not with temperature and that the rate parameter (1/alpha) varied with temperature according to an Arrhenius law, with a pressure-independent activation energy, and varied exponentially with pressure. The activation energy and the pressure-sensitivity parameter did not vary with pH up to pH 9. The results suggested a discontinuity of the kinetic behaviour at pH 10, with a different inactivation mechanism prevailing.