Thirty percent of 325 sera from Athapaskan Indians in five villages in east-central Alaska were found to be positive for antibodies of California encephalitis virus (CEV) by means of the hemagglutination-inhibition (HI) test, using CEV prototype strain 283 for hemagglutination (HA) preparation. Neutralizing antibodies were detected in 72% of the sera by means of a plaque reduction method, using CEV Jamestown Canyon strain 2235. In these tests, CEV-neutralizing substances were present in all but 1 of 94 persons tested over age 30. The serum of the single exceptional individual was positive in the HI test. Since most of the persons tested had not traveled outside Alaska, serological evidence indicates that exposure to CEV had occurred within the state. Evidence for the occurrence of arboviruses in Alaska has not been reported previously.