Current orthodoxy in research ethics assumes that subjects of clinical trials reserve rights to withdraw at any time and without giving any reason. This view sees the right to withdraw as a simple extension of the right to refuse to participate all together. In this paper, however, I suggest that subjects should assume some responsibilities for the internal validity of the trial at consent and that these responsibilities should be captured by contract. This would allow the researcher to impose a (...) penalty on the subject if he were to withdraw without good reason and on a whim. This proposal still leaves open the possibility of withdrawing without penalty when it is in the subject's best interests to do so. Giving researchers recourse to legal remedy may now be necessary to protect the science, as existing methods used to increase retention are inadequate for one reason or another. (shrink)