This article describes the role of transnational anti-apartheid activism in South Africa, Britain and the United States in generating international moral outrage over the readmission of the Medical Association of South Africa (MASA) to the World Medical Association (WMA), which had taken place in 1981 after it had withdrawn from that body in 1976. It discusses an example of a controversy where an international health organisation (IHO) lost moral authority as a result of being accused of white supremacy and a pro-American engagement in Cold War politics. At the time of its readmission to the WMA, the MASA was controversial because of its failure to strike off its membership roll one of the doctors implicated the death in detention of Black Consciousness leader Steve Biko in 1977. It details how these activists viewed the American Medical Association as having campaigned for the MASA’s readmission. The WMA’s readmission of the MASA cost the former its relationships with the World Health Organisation (WHO) and the British Medical Association – a dispute which continued until South Africa’s democratic transition of 1994. With its focus on transnational activism in relation to the WMA and the effects of activists’ allegations of racism on its internal politics, this article contributes to the literature on the history of IHOs. Ultimately, this controversy shows the deficiency of international medical professional associations as ethical arbitrators of last resort.