A hand-size monkey called Callithrix jacchus—the common marmoset—is in great demand in labs and yet almost nowhere to be found. Marmosets' small size, fast growth, and sophisticated social life were already enough to catch the eye of neuroscientists. They've now been genetically engineered to make their brains easier to image and to serve as models for neurological disorders such as autism and Parkinson's. The problem: Breeders and funding agencies didn't anticipate the surge in interest. Now, the National Institutes of Health plans to launch funding to expand marmoset research. And established marmoset researchers are working together to help new labs get animals.