Six species of wild birds were studied for their suitability as sentinels to detect the transmission of EEE and WEE viruses in the Pocomoke Cypress Swamp, Maryland. Blood specimens from birds were tested for virus and for neutralizing antibodies in tubes of primary hamster kidney cell culture. Virus isolations and serological data from bobwhite quail, white-throated sparrows, red-winged blackbirds and English sparrows indicated that transmission of WEE virus began in late July, 1968, and preceded the onset of EEE virus transmission by several weeks and that transmission of both viruses continued into November. Of the species tested, bobwhite quail and white-throated sparrows survived best. Selection and use of wild birds as sentinels are discussed.