Burrows dug by albino rats were compared with those of wild Norway rats in an outdoor pen and in observation chambers in the laboratory. Burrows, in terms of measurements, configurations, or sequential development, were indistinguishable in wild and domestic rats. Burrowing for both wild and domestic rats was unaffected by raising in outdoor burrows, by availability of nesting material, or by pregnancy. Prior experience in burrowing did make it more efficient in a second trial, which suggests that learning may have a limited role in what appears to be a behavior with a strong genetic basis. Feralization of domestic rats in the outdoor pen was especially productive in answering claims of degeneracy in these animals: Albino rats were hardy throughout climatic extremes, they maintained a stable population for two years, they constructed and lived in burrows, and they showed a vaiety of wild-type behaviors.