The pulpal response to an experimental adhesion promoter (PTP) used in conjunction with a composite resin material, Biogloss, is described, in lined and unlined cavities. Dycal was the lining and negative control material. Standardised Class V cavities were prepared in ferret canine teeth and the pulpal responses studied after 1, 2 and 4 weeks and 6 months post-operatively. Pre-treatment of cavities with PTP causes a reduction in pulpal inflammation at 7 and 14 days compared with Biogloss. There was no obvious difference at the longer time intervals. Pre-treatment with PTP delays the ingress of microorganisms at the cavity wall/material interface but does not prevent it in the long term in this situation. The effect of PTP is not altered if the fluid is allowed to dry naturally rather than by blow drying.