The toxic potential of the endodontic sealers ingredients, especially the unreacted monomer, that can irritate the periapical tissue and interfere with the healing process, thus having a negative impact on the biocompatibility of the material. The aim of this study was to evaluate the influence of three experimental endodontic sealers on cells viability in vitro. Human umbilical vein endothelial cells (HUVEC) were used. The experiments were done with solid samples and extracts of sealers in artificial saliva and water. The experiments evaluated the cytotoxicity of the residual monomers that resulted from the tested composites. The decrease in cell viability was quantified by colorimetric measurement of formazan. The components of the sealers dissolved in artificial saliva and water were determined by high performance liquid chromatography (HPLC). The HUVEC are a novelty for testing the endodontic sealers biocompatibility, with certain advantages compared to other cell types used in the literature, e.g. HELA cells, fibroblasts. The data showed that cytotoxicity was directly linked with the unreacted monomer - 2-hydroxyethyl methacrylate (HEMA) present in these composites. Two of the three formulations had little or no cytotoxic effect, which makes them suitable for further testing in order to be used in endodontic treatment.