The author presents the results of researches done at the "Stefan S. Nicolau" Institute of Virology in Bucharest on the infections induced by arboviruses. The characteristics of three tick encephalitis virus strains (two strains isolated from Ixodes ricinus and Ixodes persulcatus ticks and one from a patient with encephalitis symptoms) are given. Most of the report is devoted to the results of serological survey conducted in a human population, in several domestic birds and mammals from some districts of Romania, as well as in migratory birds from the Danube delta, with regards to the incidence of some Toga-, Bunya- and Reoviruses.