To support the maintenance of COBOL application systems, we have developed a variable classification technique that classifies program variables according to what domain entities they represent. Business application systems require frequent changes because the business rules associated with the domain entities are frequently changed. To modify the system, a source code containing variables of the same domain entity must be properly identified. Our variable classification technique supports the finding of all variables of a particular domain entity by analyzing programs. This paper describes the algorithm used for variable classification and its application to the year 2000 problem. The paper also evaluates the performance of the variable classification technique implemented in a commercial CASE tool.