The histologic response to a new retrograde root filling procedure using composite and a dentin bonding agent (Gluma) was examined in two monkeys (Cercopithecus aethiops). Infected root canals in canines and incisors were retrograde sealed and a histologic examination performed after 1 year. Among three canines, two showed epithelial proliferation on the resected root surface, apparently originating from the incision which had been placed very close to the level of resection. In the third canine, filled with a composite containing tricalciumphosphate, there was not only reformation of new Sharpey's fibers, but also, seen for the first time, regeneration of new cementum directly upon the retrograde filling material (Fig. 1). Two incisors were extracted, the apices resected, a retrofilling applied, and the incisors replanted. In this way any interference by epithelium could be avoided. After 1 year, both teeth showed a narrow fibrous zone without inflammation opposite the filling material (Fig. 2). The surprising finding that a composite could allow complete PDL regeneration including cementum upon the retrograde material implies that a new biologic retrograde root filling principle is at hand. Experiments are now in progress to further characterize the necessary condition for cementum repair upon composite used as a retrograde root filling material.