Three isolates of Jamestown Canyon virus and one isolate of snowshoe hare virus (California serogroup) were obtained from adult Aedes females collected in western Massachusetts in 1982. Jamestown Canyon virus was isolated from Aedes abserratus/punctor once, and from Aedes intrudens twice. Snowshoe hare virus was isolated from Aedes stimulans group mosquitoes. La Crosse encephalitis (LAC) virus was not isolated from 1,552 adult Aedes triseriatus, nor from 22,557 Aedes triseriatus larvae. However, sera from 1/178 eastern chipmunks, 5/31 gray squirrels, and 8/144 white-tailed deer had neutralizing antibody to LAC virus. No sentinel rabbits placed at sites yielding virus isolates seroconverted to CAL viruses in either year.