Four tick-borne arboviruses circulate heavily and permanently among the seabirds colonies located along the coasts of Brittany: Soldado, Zaliv Terpeniya, Avalon and a member of Tyuleniy subgroup of flaviviruses. In order to appreciate the ability of these viruses to infect man, the authors studied for antibodies the sera of farmers living in South-Finistere, in the vicinity of Cape Sizun seabirds reserve. Antibodies were actually found on 14 of 474 farmers, or 3.0 per cent, substantiating the reality of infection by these agents. The possible mechanisms of the contamination and the eventual pathologic results of these viral infections are discussed.