International research, sponsored by for-profit companies, is regularly criticised as unethical on the grounds that it exploits research subjects in developing countries. Many commentators agree that exploitation occurs when the benefits of cooperative activity are unfairly distributed between the parties. To determine whether international research is exploitative we therefore need an account of fair distribution. Procedural accounts of fair bargaining have been popular solutions to this problem, but I argue that they are insufficient to protect against exploitation. I argue instead that a maximin principle of fair distribution provides a more compelling normative account of fairness in relationships characterised by extreme vulnerability and inequality of bargaining potential between the parties. A global tax on international research would provide a mechanism for implementing the maximin account of fair benefits. This model has the capacity to ensure fair benefits and thereby prevent exploitation in international research.