The National Institutes of Health announced on Thursday it is planning to lift its ban on funding some research that injects human stem cellsinto animal embryos.

The N.I.H. announced its proposal in a blog post by Carrie Wolinetz, the associate director for science policy, and in the Federal Register.

Two types of experiments that are now being considered for funding would still have to undergo a review by an N.I.H advisory committee. The first is adding human stem cells to the embryos of animals except nonhuman primates like monkeys or chimpanzees, before the embryos reach a stage when organs are starting to develop. With nonhuman primates, , according to the proposal, researchers would have to wait until an embryo was further developed before adding human stem cells.

The second type of study that would get extra scrutiny involves introducing stem cells into embryos of animals other than rodents where the cells could get into and modify the animals’ brains.

This seems like it has the potential to go very wrong.