An increasing number of moral realists and anti-realists have recently attempted to support their views by appeal to science. Arguments of this kind are typically criticized on the object-level. In addition, however, one occasionally also comes across a more sweeping metatheoretical skepticism. Scientific contributions to the question of the existence of objective moral truths, it is claimed, are impossible in principle; most prominently, because such arguments impermissibly derive normative from descriptive propositions, such arguments beg the question against non-naturalist moral realism, science cannot inform conceptual accounts of moral judgements, and the conceptual is logically prior to the empirical. My main aim in this paper is to clarify and critically assess these four objections. Moreover, based on this assessment, I will formulate four general requirements that science-based arguments in favor of moral realism and anti-realism should meet. It will turn out that these arguments are limited in several ways, and that some existing arguments have been unsound. Yet it is still possible in principle for the empirical sciences to contribute to the moral realism/anti-realism debate.