this study evaluated the cytotoxic effects of 2 mineral trioxide aggregate (mta) cements - white-mta-angelus and a new formulation, mta-bio - on odontoblast-like cell (mdpc-23) cultures. twenty-four disc-shaped (2 mm diameter x 2 mm thick) specimens were fabricated from each material and immersed individually in wells containing 1 ml of dmem culture medium for either 24 h or 7 days to obtain extracts, giving rise to 4 groups of 12 specimens each: g1 - white-mta/24 h; g2 - white-mta/7 days; g3 - mta-bio/24 h; and g4 - mta-bio/7 days. plain culture medium (dmem) was used as a negative control (g5). cells at 30,000 cells/cm2 concentration were seeded in the wells of 24-well plates and incubated in a humidified incubator with 5% co2 and 95% air at 37oc for 72 h. after this period, the culture medium of each well was replaced by 1 ml of extract (or plain dmem in the control group) and the cells were incubated for additional 2 h. cell metabolism was evaluated by the mtt assay and the data were analyzed statistically by anova and tukey's test (α=0.05). cell morphology and the surface of representative mta specimens of each group were examined by scanning electron microscopy. there was no statistically significant difference (p>0.05) between g1 and g2 or between g3 and g4. no significant difference (p>0.05) was found between the experimental and control groups either. similar cell organization and morphology were observed in all groups, regardless of the storage periods. however, the number of cells observed in the experimental groups decreased compared to the control group. mta-bio presented irregular surface with more porosities than white-mta. in conclusion, white-mta and mta-bio presented low cytotoxic effects on odontoblast-like cell (mdpc-23) cultures.