Boffins plan to grow rat-human and mouse-human embryos in Japan.
The Japanese Research group has received approval from the government to insert human cells into animal embryos.
After being inserted into the animals, the cells may then grow into organs.
If research goes well, experts plan on introducing the embryos into other animals such as pigs.
“We don’t actually know what’s going to happen”
Ronald Parchem, an assistant professor of neuroscience at Baylor College of Medicine in Houston, said: “I personally thought it was very exciting.
“It has tremendous potential to help many people who are suffering from a broad variety of diseases or in need of different types of tissue or organ replacement.”
Japan made headlines when it allowed growing human cells in animal embryos.
This has allowed a number of experiments to take place, with researchers even planning a human-monkey hybrid.
Parchem told Live Science: “We don’t actually know what’s going to happen.
“Our training suggests it’s very unlikely you would get a mouse with human qualities.
“What you might find is there’s more folding in the brain or there’s more of a certain type of neurotransmitter.”
It is hoped that organs grown in the species could one day be used for humans.
He added: “Anytime you take a species and mix it with another, the host species generally does better.
“If you take a rat cell and put it into a mouse blastocyst, the rat cells are at a disadvantage. That’s why in general, chimerism is very low.”
Once the hybrid embryos develop, they will be monitored for one to two years.