Conventional dynamic debugging techniques are often restricted to machine level programs, while fully conversational compilers for powerful languages are costly to develop and will not fit into small systems. This paper describes a source-language debugging system for CORAL 66 which allows a user to run his CORAL program under teletype control, and to make changes to the source program. The changes are compiled by the debugging program and immediately incorporated into the object code. This provides a useful facility which can be added to all but the smallest systems.