The author describes improvements introduced during 1986 to the development process for the System X project, a large-scale stored-program-control telephone exchange system. Attention is given to improvements within the system testing phase of the life cycle, in particular, the methods whereby subsystem developers provide solutions to software problems identified by the system testing engineers. Software maintenance can be performed either by fixing the software object code or by editing and recompiling the software source code. The adoption of the latter approach as the standard means of maintaining software during system testing has necessitated the generation of novel management, technical, and quality procedures. This approach is now also being applied to maintenance of the in-service product.>