Eight reference California group viruses of North America were typed using sera of immune hamsters bled 21 days after a single inoculation. The complement-fixation test reactions were relatively specific, although only 2-fold differences were observed reciprocally with the closely-related La Crosse and snowshoe hare viruses. Hamster serum taken 10 days post inoculation was more specific than a 21-day serum. Specificity after second inoculation was lost with some antigens. Jamestown Canyon and South River viruses were identical by complement-fixation test and showed minor differences in the plaque reduction neutralization test.
Present address: Department of Entomology, University of Maryland, College Park, Maryland 20742.