Cyanoacrylate (CA) has been used as both a commercial and tissue adhesive. Dentists may have had the experience of patients repairing their own acrylic-based dentures using a cyanoacrylate (CA) adhesive known as 'super glue'. This study evaluated the cytotoxicity of commercial CA adhesives when fully polymerized, as well as the toxicity of substances released from polymerized commercial CA adhesives after incubation of these materials for various periods of time. Toxicity was tested on cultured oral fibroblasts. Dead cells found around the various CA-coated filter papers constituted inhibitory zones which varied from 200-1000 microns and which persisted for two weeks. Control oral fibroblasts grew to approach the wax-coated filter paper. Cell viability testing using MTT and crystal violet staining methods supported the conclusion that polymerized CA-coated filter paper released substances that are toxic to cells, while wax-coated filter paper gave the same result as the control. The crystal violet staining method was also used to investigate the cytotoxicity of various CA materials after incubation for one, three, seven and 14 days and showed that CA continued to release cytotoxic substances at about the same level for at least two weeks. It can be concluded that, if CA adhesive is used for repair of broken dentures, it will release substances which are toxic to human oral fibroblast cells. This release of substances may persist for at least two weeks.