Establishing electronic exchange of information among collaborating organisations is a key goal in the public and private sector today. The desire to reduce costs while providing higher quality of service are two main drivers for this development. Confidential information about individual clients are often part of the information to be exchanged. Today, the handling of such information is governed by increasingly stringent privacy legislations. Ensuring compliance of such legislations during cross-organisational information mediation requires advanced middleware mechanisms. In this paper, we analyse requirements on such mechanisms and describe their prototypical realisation in the application domain of health care.