The calcifications in dental pulp appeared to consist of discrete, smooth-surfaced laminated denticles and irregularly shaped, non-laminated denticles, together with a diffuse calcification characterized by small foci scattered throughout the fibrous pulp matrix. Calcification appeared to be initiated in relation to the interfibrillar matrix, collagen fibres and connective tissue cells. In each case the inorganic phases showed a distinct morphology; electron diffraction suggested hydroxyapatite. Both the laminated and non-laminated denticles had an organic matrix consisting of collagen fibres together with a background of electron dense material between the fibres. The laminated denticles appeared to grow by the addition of layers of collagen to the surface, leaving an uncalcified border zone which gradually calcified. The matrix of the non-laminated denticles was formed by the collagen fibres orientated in the long axis of the pulp, and no border zone was present. These denticles grew by the addition of mineral to the adjacent matrix fibres. Some small denticles did not have a collagen fibre matrix, but an electron-dense granular matrix was present. One such denticle was being resorbed by a giant multi-nucleated cell. The non-laminated denticles contained areas devoid of fibrils in which the crystallites were larger but gave a diffraction pattern indicative of hydroxyapatite. Between the matrix fibres in diffuse calcification an electron dense granular material was present.