In an earlier article in this journal I argued that the question of whether heroin addicts can give voluntary consent to take part in research which involves giving them a choice of free heroin does not – in contrast with a common assumption in the bioethics literature – depend exclusively on whether or not they possess the capacity to resist their desire for heroin. In some cases, circumstances and beliefs might undermine the voluntariness of the choices a person makes even (...) if they do possess a capacity for self-control. Based on what I took to be a plausible definition of voluntariness, I argued that the circumstances and beliefs typical of many vulnerable heroin addicts are such that we have good reasons to suspect they cannot give voluntary consent to take part in such research, even assuming their desire for heroin is not irresistible. In a recent article in this journal, Uusitalo and Broers object to this on the grounds that I misdescribe heroin addicts' options set, that the definition of voluntariness on which I rely is unrealistic and too demanding, and, more generally, that my view of heroin addiction is flawed. I think their arguments derive from a misunderstanding of the view I expressed in my article. In what follows I hope therefore to clarify my position. (shrink)