The purpose of this study was to evaluate the cytotoxicity of gamma-ray-polymerized poly(methyl methacrylate) (PMMA). A total of 32 disk-shaped PMMA specimens were polymerized by gamma-irradiation with 1 Mrad for 4 h (Group 1), 2 Mrad for 8 h (Group 2), 3 Mrad for 12 h (Group 3), and thermally polymerized (Group 4). Four- and 6-day eluates of the specimens were prepared in Eagle's Minimal Essential Medium (EMEM) without Fetal Calf Serum TCS). The eluates and EMEM supplemented by 20% FCS were placed into Vero (green African monkey kidney) cell cultures, and incubated at 37degreesC for 24, 48, and 72 h. EMEM kept at 37degreesC for 4 and 6 days was also tested up to 72 h, and served as controls. After each incubation period, the number of viable cells were counted and stained at the termination of the experiments for histological evaluation. The number of viable cells for Group 1 was slightly lower than that of other groups after 24 h. The time-dependent increase in cells exposed to Group 3 eluates was comparable with the control group. There was a dose-dependent effect on cell response for gamma-ray-polymerized specimens. The number of viable cells and the morphological appearance of cells in all groups were similar. Eluates from PMMA polymerized by low doses of gamma-ray with reduced polymerization periods have early inhibitory effects on cell response. Higher doses of gamma-irradiation lead to better cellular response, and therefore, may be future candidates for polymerization of PMMA.