A variety of tools, based on object-oriented design methodology, are already available commercially. Many new tools are being developed. However, tools for the design of real-time systems are still scarce. This paper presents a working environment for the development of real-time systems. This working environment is a collection of CASE tools, which are a heavy graphical orientation intended for the specification, analysis, design, and implementation of large and complex real-time systems by object-oriented techniques. It enables a user to use object-oriented techniques to prepare, analyze, and debug diagrammatic, yet precise descriptions of the objects of the system under development from five interrelated points of views: capturing environment, functionality, behavior, performance and hardware. In addition to the use of performance analysis tools, the main novelty of our working environment is in the fact that it can design real-time systems at different levels of granularity, carry out rigorous execution, simulation and animation of the described system, and create running code automatically.