This study evaluated in vitro the cytotoxicity of four root canal sealers (Topseal, EndoRez, TubliSeal and Kerr Pulp Canal Sealer E.W.T.) and their effects on reactive oxygen/nitrogen intermediate induction by mouse peritoneal macrophages. Thioglycollate-induced cells were obtained from Swiss mice by peritoneal lavage with 5 mL 10 mM phosphate-buffered saline, washed twice and resuspended (10(6) cells/mL) in appropriate medium for each test. Cytotoxicity was determined by the presence of hydrogen peroxide (H2O2) and nitric oxide (NO) by the peroxidase-dependent oxidation of phenol red and Griess reaction, respectively. Sealer suspensions were obtained in two different concentrations from each material: 18 mg/mL and 9 mg/mL, established according to compatibility parameters following MTT assay. Comparing the sealers, H2O2 release at concentrations of 9 mg/mL and 18 mg/mL was similar: Topseal > positive control (medium + cells + 5 mg/mL zimozan solution) > EndoRez > TubliSeal > Kerr Pulp E.W.T. > negative control (medium + cells). NO release at concentration of 9 mg/mL was: positive control (medium + cells + 10 microg/mL LPS solution) > Topseal > Kerr Pulp E.W.T. > TubliSeal = EndoRez > negative control (medium + cells); at concentration of 18 mg/mL was: positive control > Topseal > Kerr Pulp E.W.T > TubliSeal > EndoRez > negative control. Based on the results, it may be concluded that Topseal presented the highest cytotoxicity among the tested sealers, releasing higher concentrations of NO and H2O2 in macrophage culture.