To assess the biocompatibility of an adhesive system, standard Class V cavities were prepared in vivo in human premolars that were to be extracted for orthodontic purposes. Histologic observation revealed that the Gluma Bond System elicited slight to severe pulpal responses, altered odontoblastic layers, and inhibited dentinogenesis. These alterations were observed after in vivo periods of up to 120 days. In this experiment, the dentinal adhjesive was polymerized separately from the composite resin, a procedure not recommended by the manufacturer. This may explain the differences in the present results and those reported by the manufacturer.