DEET, N,N-Diethyl-meta-toluamide is the most common active ingredient in insect repellents. It is a chemical applied to the skin or clothing that is used to protect against arthropods such as ticks and mosquitoes. We did preliminary experiments that showed the surprising result that DEET kills mosquito cells in tissue culture. This was unexpected because cultured cells do not have sensory organs to detect a repellent. While running SDS gels we discovered a protein that was expressed in cells that were treated with DEET and absent in those that were not.