In the present study, I investigated the effects of N-methyl-D-aspartate (NMDA), arachidonic acid (AA), and Nitric Oxide Synthase Inhibitor (NOS-I), alone or in combination, on the viability of cultured primary normal human oral keratinocytes (NHOK). Specifically, we examined whether AA and NOS-I could protect primary NHOK from glutamate cytotoxicity. The purpose of this study was therefore the preliminary study for the examination of the interaction between these agents and NHOK in order to elucidate the mechanisms by which epithelial growth and regeneration are regulated. NHOK were obtained from gingival tissue of 20 individuals aged 20 to 29, and third passage (P3) cells were used for this study. Cell viability was measured by the MTT assay. NMDA and NNA, a calcium dependent NOS inhibitor, induced an initial increase in cell number, which subsequently decreased by the $7^{th}$ day. Low concentration of AA ($0.5;{mu}M$ & $1;{mu}M$) induced an increase in cell number while high concentrations of AA ($5;{mu}M$ & $10;{mu}M$) induced a decrease in cell number. The decrease in cell number induced by NMDA at the $7^{th}$ day was abolished by the addition of low concentrations of AA ($0.5;{mu}M$ & $1;{mu}M$) or NOS inhibitors. Low concentrations of AA ($0.5;{mu}M$ & $1;{mu}M$) or NOS inhibitors may protect the NHOK from NMDA induced cytotoxicity. These reactions might be related to the NMDA receptor in the cell and the change of the intracellular calcium ion concentration.