Sero-epidemiological survey for Arboviruses among Bi-Aka Pigmies of the Lobaye, Central African Empire. A sero-epidemiological survey has been conducted, in 1975-1976, among 349 nomadic Pygmies of the Lobaye area in the Central African Empire, to investigate the prevalence of arbovirus infections. The percentages of individuals with detectable antibodies were 9,5 % for Chikungunya, 13,5 % for Semliki Forest, 5,2 % for Sindbis; 11,7 % for Bunyamwera; 2,3 % for West Nile, 6,3 % for Uganda S, and 8,9 % for Yellow Fever. These results are similar to those found in 1964 by CHIPPAUX in a comparable group of Pigmies of the same area and confirm that the prevalence of arbovirus infections is lower in the nomadic pygmies of the same area and confirm that the prevalence of arbovirus infections is lower in the nomadic Pygmies than in the sedentary Pygmies as well as in the settled bantus of the Lobaye valley villages. Yellow fever specific antibodies detected in this non vaccinated population indicate that latent infections occur in human beings living in the depth of the tropical forest, from the natural sylvatic focus of yellow fever, which remains active as recently proven in the Central African Empire by virus isolations obtained from wild caught mosquitoes.