Changing customer needs and computer technology are the driving factors influencing software evolution. There is a need to assess the impact of these changes on existing software systems. Requirement specification is gaining increasingly attention as a critical phase of software systems development process. In particular for larger systems, it quickly becomes difficult to comprehend what impact a requirement change might have on the overall system or parts of the system. Thus, the development of techniques and tools to support the evolution of requirement specifications becomes an important issue. In this paper we present a novel approach to change impact analysis at the requirement level. We apply both slicing and dependency analysis at the Use Case Map specification level to identify the potential impact of requirement changes on the overall system. We illustrate our approach and its applicability with a case study conducted on a simple telephony system.