The occurrence and distribution of the regulatory peptide endothelin in normal and inflamed human dental pulp was studied by immunocytochemistry. Endothelial cells in both normal and inflamed pulp displayed endothelin-like immunoreactivity. Neither pulp cells nor dental nerves were immunoreactive. No significant change in the distribution of endothelin immunoreactivity could be detected in the samples of inflamed pulp tissue, the immunoreactive material being detectable only within the endothelium. However, the intensity of the immunostaining was less intense in the samples of inflamed pulp. It is reasonable to presume that endothelin, produced and released locally by endothelial cells, may participate via a paracrine mechanism in the regulation of blood pressure and flow in normal and pathological human dental tissues.