The State of Iowa maintains a continuing surveillance program for the detection of arbovirus activity. Results of laboratory studies of avian, human, and mosquito specimens collected during the summer of 1977 are presented. Cache Valley, Flanders, trivittatus, Turlock, and western equine encephalomyelitis arboviruses were isolated from 73 of the 613 pools of mosquitoes examined. Avian blood specimens collected from 41 species were examined for St. Louis encephalitis (SLE) and western equine encephalomyelitis (WEE) hemagglutination-inhibition (HI) antibodies. Both SLE and WEE antibodies were detected among the 1,037 avian sera tested. One case of WEE and three cases of California encephalitis in humans were serologically confirmed and are discussed. A survey to determine the incidence of encephalitis in equines revealed arbovirus activity throughout the state.