Paying research subjects as an incentive to participation is a widespread practice within health and social research. Where subjects are illegal drug users, this practice is often felt to raise particular ethical issues. This paper explores this question of paying drug users to take part in research from the perspective of three models: justice; human rights; and business. Issues discussed include whether cash payments are appropriate, payment amounts, whether incentives jeopardize informed consent and whether they offer good value-for-money for research funders. Some practical implications of the discussion are set out and four key components for good practice are proposed. Finally, in conclusion it is argued that the use of incentive payments in drugs research needs to be more fully and openly debated by researchers, research funders and other stakeholders. © 2005 Taylor & Francis Group Ltd.