In a prospective field study conducted from July 2000 to June 2001, adult Aedes aegypti and Ae. albopictus mosquitoes were caught from the municipality of Nova Iguaçu, State of Rio de Janeiro, Brazil. Virus isolation in Ae. albopictus clone C6/36 cell line and a semi-nested reverse transcription-polymerase chain reaction detected only dengue virus type 3 in three pools of Ae. aegypti, despite the co-circulation of DEN-1, DEN-2 and DEN-3 serotypes in that area. No viruses were detected in Ae. albopictus mosquitoes. This virological surveillance consists in a sentinel system alerting for dengue outbreaks.