The purpose of the present investigation was to compare histologically pulpal reactions beneath inlays cemented with either a zinc phosphate or a polycarboxylate cement. No inflammatory reaction was seen beneath any of the 39 deep cavity preparations in teeth without pulpal lesions and with an inlay cemented with polycarboxylate cement. In the contralateral teeth, under 39 inlays cemented with zinc phosphate cement, an inflammatory reaction was seen beneath two cavity preparations. In one, bacteria were found on the floor of the preparation. On the basis of this result and the findings of our earlier investigations, it may be warranted to conclude that neither the polycarboxylate cement nor the zinc phosphate cement has any notable irritating effect on the pulp. If the irritation occurs after cementation of the restoration, it may be caused by debris containing bacteria and left behind on the prepared surfaces by bacterial growth from the surface of the tooth. The findings underline the importance of removing grinding debris and bacteria before cementation of the restoration.