The aim of this study was to evaluate the clinical values of calcium phosphate ceramics from the biological point of view. Two kinds of calcium phosphate ceramics, tricalcium phosphate (TCP) and hydroxyapatite (HAP) ceramics with a low sintering temperature (LT) and a high sintering temperature (HT), were applied to exposed pulp wounds in ninety healthy human teeth. Each group was further subdivided into 2 groups with selected granule diameters of 5 microns (S) and 40 microns (L), and investigated clinico-pathologically. Clinically, cases showing some kinds of discomfort symptoms comprised 3/15 of the TCP (S) group, 3/15 of the TCP(L) group, 3/15 of the LT(S) group, 4/15 of the LT(L) group, 2/15 of the HT(S) group, and 3/15 of the HT(L) group. The symptoms were generally slight or very slight and disappeared within eight days in the LT(S) group. Histo-pathologically, inflammatory reactions were observed within 2 weeks. Traumatic injury caused by surgical wound or by mechanical irritation from the materials produced various pathological changes. After the treatment, pulp manifested reparative changes such as cicatrization, formation of new denticles, and dentin apposition on pulp-chamber walls. In many cases, TCP and HAP produced similar effects on human dental pulp. In the TCP(S), the LT(S), and HT(S) groups, a calcified matrix had appended by 3 weeks. In TCP(L), LT(L), and HT(L) groups, the matrix had appended from 3 to 6 weeks. Calcified matrix formation in the LT group was slightly less than in that in the HT of HAP group. In a few cases, complete dentin bridges formed over the exposed pulp surfaces. These results suggest that HAP (both LT and HT) and TCP ceramics are biocompatible and do not harm human dental pulp. These ceramics were found to be clinicopathologically effective in biologically protecting exposed human dental pulp and useful as basic materials in endodontic therapy.