We adapted the Seliwanoff method to quantify fructose in mosquitoes. This method showed a minimum detection limit of 2.4 microg of fructose, and was more reliable and nearly four times more sensitive than the anthrone test. The Seliwanoffmethod was used to measure the maximum sugar intake by individual mosquitoes and to determine the digestion time of this nutrient by both Aedes aegypti and Aedes albopictus in the laboratory. Sugar intake by Ae. albopictus was up to 1.7 times higher than that of Ae. aegypti. The amount of sugar ingested by females was up to 2.5 times higher than that of males in both species. After 48 h, a fructose meal was not detected any longer in either species. The Seliwanoffmethod was applied to measure fructose content of field-collected Ae. aegypti males and females in Rio de Janeiro. Results showed that even Ae. aegypti females do feed on sugars. The standardized Seliwanoff method proved to be reliable for measuring the sugar content of individual mosquitoes and can be used wherever estimation of small quantities of fructose is needed.