Amalgam restorations have been replaced for composite ones in the last few years, mainly because of the known harmful effects of mercury on health. But, these new restorative materials are not entirely safe either. Some recent studies have proven that some monomers released from dental composites may have adverse effects such as allergy reactions, DNA damage, besides protein and DNA synthesis inhibition. The present study evaluated the effect of triclosan (TRN) and chlorhexidine (CHX) on monomer release from four different composites commercially available, namely: Z100, TPH, Charisma and Durafill. Eighteen specimens were prepared for each brand, randomly separated into three groups: control (phosphate buffer 0.1 mol/L, pH 7.4), TRN 0.3% or CHX 0.12% both in phosphate buffer 0.1 mol/L, pH 7.4. The samples were incubated for 24h at 37^oC. After incubation, supernatant was collected and 10 mL were analyzed by HPLC, using a C-18 column, flow rate at 1 mL. min^-1 with an acetonitrile/water gradient. In general, two main peaks were observed on the chromatograms for all composites independently of the presence of TRN or CHX. Among the brands, TPH showed to release the smallest amount of products, while Charisma and Durafill released the largest amount of products. In order to identify the chemical structure of the released products, electrospray/tandem mass spectrometry analysis were performed. The fragmentation spectrum showed a signal pattern that was distinctive of TEGDMA, a co-monomer present in these composites. The other product was identified as TEGMA, which corresponds to TEGDMA unit hydrolyzed by one ester bond. These compounds have a cytotoxic pontential, promoting mainly membrane damage. In conclusion, we showed that there are some differences in the amount of the released compounds among the brands analysed in this study, these compounds were identified as TEGDMA and its hydrolysis product, TEGMA. Finally, the treatment with TRN or CHX did not caused significant changes in the kind of the released products from the composites studied. Supported by CAPES and CNPq.