Surveillance programs initiated in response to the 1999 West Nile virus (WNV) outbreak have detected increased transmission in the northeastern United States (1). Seventeen states along the Atlantic and gulf coasts, New York City (NYC), and Washington, D.C., have conducted WNV surveillance and are reporting to CDC (1). Surveillance for WNV infection includes monitoring of mosquitoes, sentinel chicken flocks, wild birds, and potentially susceptible mammals (e.g., horses and humans) (2). This report summarizes findings of this surveillance system through August 7, 2000.