This paper proposes an approach for reusing requirements, focusing on the use cases' specification. The approach proposes a method, called M-4REuse, which integrates several existing techniques and concepts of reuse, such as use case fragments, catalogue, assembling variability of use cases starting from aspects. To support the proposed method, a tool called 4REuse available on the web was developed. A study was conducted to evaluate the usability of 4REuse within classes in Brazilian universities. We believe that this approach will allow novice requirements professionals to write high quality use cases in less time than when using other approaches, through the use of variability in use case fragments.