Inadequate requirements specification is one of the main causes of software development project failure today. A major problem is the lack of processes, techniques and automated tool support available for specifying system requirements. We suggest a way to improve requirements specification methodology by enhancing the approach that is most popular at the moment - use case modelling. Despite their popularity, use case models are not formal enough for automated analysis. We amend traditional use case models with a formal structure and semantics to make them suitable for automated verification. The enhanced use case modeling technique that we propose is called Susan (”S”ymbolic ”us”e case ”an”alysis) and it facilitates verification of use case models using symbolic model checking. We also developed a software tool called SusanX to construct, manipulate and analyse Susan models. The analysis feature of the tool is implemented using the NuSMV model checker. A number of generic properties for verification are built into SusanX, and the tool additionally allows the user to construct model-specific properties