Aedes provocans were allowed to feed on a bloodmeal containing 5.6 log10 TCID50/ml of Jamestown Canyon (JC) virus. After 14 days of incubation at 21 degrees C and 80% RH, 100% (36/36) were midgut infected, 50% (18/36) developed disseminated infections and 50% (9/18) of the latter specimens transmitted virus to capillary tubes. When mosquitoes were intrathoracically inoculated with 6.1 log10 TCID50/ml of JC virus, 100% (40/40) became disseminated infected and 95% (38/40) transmitted virus after 12 days of incubation. A midgut escape barrier was recognized as the major barrier to JC virus transmission in orally infected Ae. provocans.