Separation of concerns, which aims at separating different aspects involved in complex applications, is a general trend in software programming. It allows a given aspect to be programmed in a more or less isolated manner from the functional code of an application. This trend has been studied by the AOP (Aspect Oriented Programming) community, through the provision of language supports for programming and composing aspects. It has also been experi-mented in the context of component-based middleware, which usually address system-related aspects (e.g., transactions, security, persistence, etc). In both domains, most implementations of separation of concerns involve indirection objects and extra method calls that incur a non-negligible performance over-head. While performance was initially not the main motivation of «separation of concern environments», we believe that it is possible to efficiently integrate as-pects in such environments. In this paper, we report on an experiment which aims at optimizing aspects through code injection techniques. We consider two aspects, replication and access control, and present a preliminary performance evaluation which confirms that the overhead can be significantly reduced.