The hemagglutination-inhibition test was used to detect antibodies to influenza virus of swine in Hawaii. Antibodies were detected in swine from 25 of 63 farms tested. Epizootiologic studies indicate that severe respiratory disease is not known to occur on swine farms in Hawaii. It can be concluded that influenza in swine does occur in Hawaii and furthermore that the infection occurs only in a mild or subclinical form. This study suggests that influenza in swine is probably more widespread in the United States than has been previously suspected.