Aedes bahamensis, a recent introduction to the state of Florida, was studied to determine its capability to serve as a host or vector of St. Louis encephalitis (SLE) virus. Females were readily infected by inoculation, and had whole body virus titers as high as 10(9.4) mosquito infectious doses 50. Sixty percent of females that had been infected by inoculation were capable of orally transmitting virus. Nearly half of the females feeding on viremic chickens became infected, but not all of these infections disseminated to the head. Vertical transmission of SLE virus to progeny of inoculated females was also demonstrated.