Software developers create a variety of artifacts that model viour of applications at different levels of abstraction; e.g. use cases, sequence diagrams, and source code. Aspect-oriented programming languages, such as AspectJ, support the modularization of crosscutting concerns at the source code level. However, crosscutting concerns also arise in other behavioural models of software systems. We provide a new aspect language, AspectU, which supports modularization of crosscutting concerns in the use-case model. Further, we provide a prototype tool that partially translates AspectU aspects into AspectJ aspects. To facilitate this translation we introduce a third aspect language, AspectSD, which targets the sequence-diagram model. AspectU together with our translation tool allows developers to express advice using use case level concepts while still affecting the runtime behaviour of a system, yielding a natural and intensional expression of some concerns.