Interaction of chlorhexidine with biomembrane models on glass ionomer by using the Langmuir-Blodgett technique. The antimicrobial property of chlorhexidine is believed to be associated with its interaction of bacterium membrane, which calls for research on the identification of membranes sites capable of drug binding. In this study, we investigated the interaction of chlorhexidine digluconate, a known agent with bactericidal and bacteriostatic activities employed in the treatment of periodontal diseases, with bacteria cell model systems by using Langmuir monolayers. The insertion of the drug caused the surface pressure-area isotherms for a mixed protein-lipid monolayer to be shifted to higher lipid molecular areas, which was the first indication of the action of chlorhexidine in the membrane model. Surface infrared spectroscopy pointed to intrinsic interactions of the drug with the hydrophobic part of the lipid, leading to a disruption of the lipid organization at the interface. Also, the secondary structure of the polypeptide model employed in this work has been changed, as a consequence of the drug interactions. Such change in the lipid-protein models could be confirmed when the membrane was transferred to glass ionomer cement as a solid support, which can be considered a model for dental surfaces. Therefore, chlorhexidine interacts with lipid and protein moieties supposed to be present in lipid membranes. This may have important implication in understanding how the drug acts on specific sites of the bacteria membrane.