Participants in research and development alliances face a difficult challenge: How to maintain sufficiently open knowledge exchange to achieve alliance objectives while controlling knowledge flows to avoid unintended leakage of valuable technology. Prior research suggests that choosing an appropriate organizational form or governance structure is an important mechanism in achieving a balance between these potentially competing concerns. This does not exhaust the set of possible mechanisms available to alliance partners, however. In this paper we explore an alternative response to hazards of R&D cooperation: reduction of the of the alliance. We argue that when partner firms are direct competitors in end product or strategic resource markets even protective governance structures such as equity joint ventures may provide insufficient protection to induce extensive knowledge sharing among alliance participants. Rather than abandoning potential gains from cooperation altogether in these circumstances, partners choose to limit the scope of alliance activities to those that can be successfully completed with limited (and carefully regulated) knowledge sharing. Our arguments are supported by empirical analysis of a sample of international R&D alliances involving electronics and telecommunications equipment companies.