Mono-, di-, and trimethacrylates (monomers) are widely used in dentistry as restorative materials, adhesives, prosthetic devices, etc. It is known that the residual monomers released from the cured resin have been implicated in toxicological effects.' In order to monitor the biological actions at the membrane level induced by monomers, we studied the changes in the phase transition temperature ( r ) and enthalpy (AH) of dipalmitoyl-phosphatidylcholine liposomes induced by 37 different monomers using differential scanning calorimetry (DSC). The monomers that caused large changes in the T and AH were vinyl monomers; acrylates; monomethacrylates that contain hydroxy, carbonyl, amino and phenyl groups; dimethacrylates with short-chain substituents; and aliphatic trimethacrylates. It is suggested that the changes in the T and AH values may be due not only to hydrophobic interactions, but also to interactions induced by the double bonds or the functional groups in the monomers. On the other hand, methacrylates with simple alkyl ester linkage and dimethacrylates with bisphenol A groups exhibited the smallest changes. The changes in the T and AH induced by highly hydrophobic methacrylates were small due to their slower interaction. These changes in transition properties of liposomes seem to be related to biolgical activities.