Arbovirus infections are of public health interest in East Africa, where a very widespread epidemic of o'nyong-nyong fever was reported in 1959-60 and where the threat of yellow fever, present in neighbouring areas such as Ethiopia, remains. Sera collected in a serological survey in Kenya were therefore tested for antibodies against 3 group-A arboviruses (chikungunya, o'nyong-nyong and Sindbis), 6 group-B arboviruses (Zika, yellow fever, West Nile, Banzi, Wesselsbron and dengue 1), and Bunyamwera virus. The sera were examined mainly by the haemagglutination-inhibition test but a small proportion were also subjected to virus neutralization tests.The results showed that the prevalence of arbovirus tnfection varies markedly from area to area in Kenya. All types of arbovirus infections were more frequent on the coast than on the dry plateau around Kitui and the Lake Victoria area, The only exceptions were o'nyong-nyong and chikungunya, which were found to be just as prevalent on the coast as in Nyanza, where an epidemic was reported in 1959-60. Yellow fever antibodies were found to be present in about half of the people living on the coast but practically absent from the other two areas. It was concluded that the yellow fever antibodies in the coastal area must be due either to vaccination or to cross-reactions with other group-B arboviruses.