Immunoelectron-microscopy was applied to reveal the existence of nerve fibres and terminals showing calbindin D28k (CB)-like immunoreactivity (IR) in the rat molar tooth pulp. In the root pulp, thick, smooth-surfaced CB-IR nerve fibres were in bundles accompanying the blood vessels. In the coronal pulp, the fibres arborized repeatedly and extensively. CB-IR nerve fibres had a predominantly thick, smooth-surfaced appearance, though parts appeared thin and beaded. Occasionally some thin, varicose CB-IR nerve fibres ran along the odontoblasts, penetrating into the predentine alongside the dentinal tubules. They could be traced for approx. 10-20 microns into the predentine from the pulp-predentine border. Immunoelectron-microscopy revealed that only some of the nerve terminals in the predentine showed CB-IR, and that predentinal CB-IR nerve terminals were located close to the odontoblast processes. No synaptic structures were observed between them. The presence of CB-IR nerve terminals in the predentine suggests that many, if not all, CB-IR nerve fibres could be nociceptors. The CB could be involved in Ca2+ homeostasis during the activation of nociceptors.