This article describes a method of user interface reengineering used in a project of turning a large character based archaic DOS application into a modern Windows application. The program was originally written for mainframe environment in COBOL language. During the conversion the working core had to be left unchanged. In the applied method the original program - recompiled for Windows with the I/O calls replaced - is run and remote controlled through a communications module by the new wrapping application. The new program, the Artificial User Program was developed with S-Prog, a highly effective visual tool. Some parts of the source were generated by Word Basic macros.