Technical Abstract: Observations on the behavior of Aedes aegypti, Anopheles stephensi mosquitoes and the sand fly Phlebotomus papatasi in the presence of Deet, SS220, and Picaridin® topically applied to the skin of human volunteers showed that the insects were deterred from feeding on and repelled from surfaces emanating these compounds. When offered a 12 cm2 area of skin, one half treated with compound and one half untreated, the female insects fed almost exclusively on untreated skin. The sand fly and the mosquitoes detected treated surfaces without flight searching or by touching the skin surfaces. When the respective skin areas were covered with cloth, to prevent insect contact with skin surfaces, insects landed on and intensively bit through cloth covering untreated skin. This proved that the chemicals deterred insect feeding as a result of compound perceived in the vapor phase rather than by a tactile interaction with chemical. When cloth, one half untreated and the other half treated with chemical, was placed over untreated skin, the insects bit through the untreated cloth and avoided the treated cloth. In the presence of any of the three chemicals, no matter how presented to the insects, overall biting activity was reduced by about 50% relative to controls. This reduction evidenced a repellent effect for the compounds. Despite the fact that Deet, SS220 and Picaridin are often called insect repellents, they should also be classified as feeding deterrents because data show that they exert both effects upon the behavior of mosquitoes and sand flies. Heretofore, the combined effects of these compounds was not known.