Surgical biopsies from 2 human craniopharyngiomas were transplanted subcutaneously into 6 athymic "nude" mice. Morphologically characteristic craniopharyngiomas grew in 5 of these animals. In 4 animals growth was sufficient to allow transplantation into a second generation of animals. In all, 11 craniopharyngiomas were present at autopsy in the 14 animals into which the tumors had been transplanted. The tumors that grew in the animals had the same adamantinomatous architecture, epithelial nests, and keratinized nodules that were present in the original surgical sample and that are characteristic of human craniopharyngiomas. It may be possible to study growth characteristics and therapeutic sensitivities of human craniopharygniomas growing in "nude" mice.