Purpose: This study investigated the cytotoxicity of a high-noble alloy (Bioherador N) and six commercially available base-metal alloys, including four Ni-Cr alloys (Remanium CS, Heranium NA, Wiron 99, CB Soft), one Co-Cr alloy (Wirobond C), and one Cu-based alloy (Thermobond). Materials and Methods: Ten specimens from each alloy were prepared in the form of disks, which were placed in 24-well tissue culture plates together with a suspension containing Balb/C 3T3 fibroblasts (5 = 105 cells/mL). After 3 days of incubation at 37°C, cell viability was determined by the MTT method. Results: Variations in cytotoxicity of the alloys were observed and related to their composition. One-way ANOVA showed statistically significant differences in cytotoxicity of the alloys (P .001). Tukey's multiple comparisons (>= = .05) revealed that Bioherador N was significantly less cytotoxic than all the other alloys. Thermobond was the most cytotoxic, followed by CB Soft, and both of these alloys were significantly more cytotoxic than all the others. Conclusion: The cytotoxicity of casting alloys tested in this study was markedly affected by their composition. Differences were found in the cytotoxicity of alloys classified within the same category. The presence of Cu in the composition of the alloy adversely affected cell viability.