The current proliferation of light-polymerized denture base resins and the continual modification of their formulations make standardized biocompatibility testing a necessity. The biocompatibilities of three light-polymerized denture base resins were compared using an in vitro epithelial cell culture system. The effect of varied lengths of polymerization of denture base resin on cell toxicity was examined. This study indicated that light-polymerized denture base resins have an effect on oral epithelial cells that appears to be related to the specific formulation of the material and not to the type of polymerization required. Varying the polymerization time or light-polymerization unit appeared to have little effect.