The US National Institutes of Health (NIH) is seeking public comment on proposed changes to the way it funds research into animal embryos containing human cells. The proposal, announced on August 4, would lift a funding moratorium issued by the agency last October on research involving certain types of human–animal chimeras (Nat. Biotechnol. 34, 124–125, 2016). The policy changes are aimed at updating guidelines for funding chimeric animal model research in view of the advances made in stem cell biology. The agency is proposing to set up an in internal steering committee, independent of the peer review process, to monitor new developments in this field and give 'programmatic input' into funding decisions. The committee will advise on two areas: research using human pluripotent cells introduced into nonhuman vertebrate embryos, up through the end of gastrulation (with the exception of nonhuman primates), and research in which human cells are introduced into post-gastrulation nonhuman mammals (excluding rodents) where the animal's brain function might be altered by the human cells. Chimeric organisms comprise admixtures of genetically distinct cells. Early-stage embryo chimeras are deemed to be of more concern that chimeras created using differentiated cells; and chimeras made with tissues from nonhuman primates raise more ethical issues than those based on species more distantly related to humans. The NIH is also proposing to modify current guidelines (set out in 2005 and amended in 2009) to expand a prohibition on the introduction of human pluripotent stem cells into blastocyst-stage nonhuman primate embryos, to include the pre-blastocyst stage. Public comments were due before September 4. In the interim, the blog post from the NIH's associate director for science policy Carrie Wolinetz in which the proposals were described received overwhelmingly negative comments from mostly (what appear to be) nonscientists.