In a serological survey for arboviruses carried out in 8 areas of Uganda between 1967 and 1969, altogether 1869 human sera were tested with 8 antigens by the haemagglutination-inhibition (HI) test. Mouse neutralization tests (NT) with Group-B viruses were also performed on selected sera.The prevalence of arbovirus antibodies was found to vary considerably between the different areas. Very few people in the highland area of Kigezi had antibody to any of the antigens used, whereas more than half of the sera from the Madi area near the Nile had antibody to several antigens. The chikungunya antibody prevalent in the West Nile, Madi and Bwamba areas is thought probably to represent previous infection with the cross-reacting o'nyong-nyong virus. Bunyamwera antibody was also highly prevalent in Madi (66.7% of children's sera and 81.5% of adult sera).The combined HI and NT results indicate that yellow fever continues to be infrequent in Uganda (only 31 sera had yellow fever neutralizing antibody); there is no evidence of recent yellow fever infection in Bwamba, an area in which this disease was previously considered endemic.