The present contribution investigates the influence of heat and mass transport effects on the uniformity of a high-pressure induced inactivation. It is based on mathematical modelling and numerical simulation. The inactivation of E coli suspended in packed UHT-milk carried out in a batch process with water as pressure medium is taken as a model process. The principal results show, that the effective inactivation rate increases with the geometrical scale of the high-pressure vessel. Significant non-uniformities of more than one log cycle in the residual surviving cell concentration can be observed depending on the package material parameters, on the position and on the arrangement of the packages in the vessel. Furthermore, the process cycle can be shortened since the effective inactivation rate is larger. (C) 2003 Elsevier Science Ltd. All rights reserved.