A comprehensive and graphic computer simulation program for retort thermal processing was developed using the Microsoft Visual Basic language. It was designed to be applicable to different retort thermal processing systems such as constant and variable retort temperature processing with different types of foods such as solids, liquids, and liquids containing particles in containers of different shapes and sizes. Finite difference and analytical models were used to solve the governing differential equations for heat penetration by conduction and convection, respectively. A numerical integration method was used for the calculation of lethality values and quality retention. The results of computer simulations using this program were compared to a conventional formula method. The agreement between the outputs from computer simulation and conventional formula method was excellent and consistent under different processing conditions, meaning that the program is accurate and reliable. The initial driving force to develop this computer simulation program was to provide data for training and testing of artificial neural artwork models and genetic algorithms for process characterization and optimization. However, the developed program can be employed for applications such as process design, validation and optimization, or for research purposes such as the investigation of intrinsic relationships between various input and output variables, and the determination of critical control points. (c) 2006 Elsevier B.V. All rights reserved.