The effects of cell density, exposure time and assay method on evaluation of cytotoxicity of chemicals were investigated using an in vitro test with extraction.L-929 cells, seeded at 4×10^3cells/ml, 2×10^4cells/ml and 1×10^5cells/ml were exposed for 1, 3 and 5 days to 8 metal salts.The 50% cell inhibitory concentration values(IC_<50>)increased with cell density but decreased with exposure time.Of the four assay methods examined, the neutral red and MTT methods were found to be useful in evaluation of cytotoxicity of chemicals.The gradient obtained from IC_<20> and IC_<80> values of the concentration-response curves was dependent upon the kinds of metal ions, cell density, exposure time and assay methods.These findings are applicable to the evaluation of the cytotoxicity of dental materials.