The influence of 18 dental materials on the activity of esterases isolated from human whole saliva has been studied. Eugenol on its own was a strong competitive inhibitor of the esterases II-2a (Ki = 3.3/10(-5) M) and II-2b (Ki = 4.7/10(-6) M). Except for Luralite all the materials that contained eugenol as one of the components (IRM, Nobetec and Opotow) were noncompetitive inhibitors. Additional in vitro inhibitors were: Adaptic, Aspa, Coe-pack and the amalgam ANA 68. Treatment with Nobetec packs in vivo resulted in a decrease activity of whole saliva.