Introduction: Polymethylmethacrylate is a material used in prostheses that can cause adverse reactions associated to residual monomer release. This release is influenced by the polymerization method. Objectives: To compare, in vitro, cell viability (CV) of two acrylic resins, one with conventional thermal polymerization [ProBase®Hot (PBH)] and another with injection [IvoBase®System (IBS)]. Materials and Methods: Resin disks (n = 4) were incubated in a culture medium (30 minutes, 24 hours, 7 days, 14 days, 1 month). 200 μL of the extract were placed in contact with 3T3 mouse fibroblasts and the MTT test evaluated CV. The results were compared with ANOVA one-way and T-student tests, with p 0.05. Results: In PHB the VC at T14 was significantly lower than the other times and in IBS T0 and T30 presented significantly lower CV values (p0,05). There was no significant difference between the two resins for most of the times studied (p=0,012) except for T30 in which IBS cell viability was significantly lower than PHB (p˂0,05). Discussion: The small differences detected between the two resins studied suggest that the amount of residual monomer released doesn't significantly influence CV, for the contact times and amount of material used in the present study. Conclusion: The type of polymerization didn't have a significant effect on CV. According to ISO 10993-5: 2009, the CV values of the present study indicate that the resins studied are not considered cytotoxic. Keywords: cytotoxicity, acrylic resins, polymerization method, biomaterials, MTT test, cell viability, polymethylmethacrylate