Mosquito attraction responses to substances collected from human skin and placed on glass petri dishes were studied. Mosquito response varied according to the source of the substance. Substances removed from the head and hands elicited the greatest attraction response in laboratory-reared mosquitoes. Mosquito response lasted up to 6 h when the substance was aged and was increased by warming the samples from ca. 25 degrees C to 37 degrees C. Of the 12 mosquito species studied, attraction response was greatest in Aedes aegypti. It is cautioned that residues deposited by handling traps or other apparatus used in mosquito studies may influence test results.