COBOL is still an important language for building mission critical enterprise systems, and there is huge amount of existing COBOL programs. We have been developing an aspect-oriented COBOL and its development environment. We are applying aspect orientation to strengthening internal control in enterprise information systems. Understanding existing COBOL programs is critical for applying aspect orientation to them, because programmers are not able to write aspects without understanding the existing programs. We have developed an environment for understanding existing COBOL programs and developing COBOL aspects. This paper describes the environment and a experience of applying it to improve internal control implemented in a small information system. Categories and Subject Descriptors D.2.5 [Software Engineering]: Testing and Debugging--code inspections and walk-throughs; D.2.6 [Software Engineering]: Programming Environments--programmer workbench General Terms Languages, Design Keywords ...