This paper examines the planning, execution, and closure of the US–Korea Cooperative Ecological Survey project in the Korean Demilitarized Zone (DMZ) in the 1960s. In this period, the U.S. National Academy of Sciences (NAS) initiated bilateral scientific cooperation between the NAS and similar organizations in developing countries along the line of the developmental turn of U.S. foreign assistance. Working closely with the NAS, U.S. conservationists used this scheme to introduce nature conservation practices and the discipline of ecosystem ecology to developing countries. In this context, by way of the NAS's Pacific Science Board, two countries' biologists initiated the preliminary cooperative project in the DMZ in 1966. Korean and U.S. scientists soon began to realize that their collaboration was marked by dissonance. The U.S. side attributed the cooperation failure to Korean culture while the Korean side criticized the unequal structure of their cooperation. Joining the global historiography of Cold War scientific collaboration, this paper pays particular attention to the intermediaries of the collaborative project and their rivalry. It argues that political struggles revolving around the position of go-betweens – as what I call knowledge brokers – on the recipient side provoked contestation between American and Korean scientists. The contention between the two sides played out in the collaboration coming to an end, albeit partially. Throughout this analysis, this study suggests paying more serious attention to the politics of scientific exchange among actors on the recipient side as an outset from which to analyze the heterogeneity of the Korean side without losing sight of their active role in the building process of American hegemony. [ABSTRACT FROM AUTHOR]