As wide-area open networks like the Internet and intranets grow larger, mobile agent technology is attracting more attention. Mobile agents are units of software that can deal with environmental changes and the various requirements of open networks through features such as autonomy, mobility, intelligence, cooperation, and reactivity. In addition, some people consider the agent technology as a promising solution to the reuse issue because of the aspect of the agents as highly adaptable software components. However, since the usual development methods of secure mobile agent applications are not sufficiently investigated, the technology is not yet widespread. In this paper, we propose a formal framework that supports mobile agent application development and reuse with consideration of the trade-offs between the security issues and the performance issues. In our framework, we design a mobile agent application by building a computational cost model and a security model, and combining patt...