A newly arbovirus prototype IPD/ A 252 has been isolated frona a batch of mosquitoes captured in 1962 in a small Senegalese village near Tataguine. The strain proved serologically different from the 44 African arboviruses to which it was compared. It is therefore temporarily classed in the non-grouped mosquitoe-transmitted arboviruses. In the village where the mosquitoes were captured, a high percentage of the inhabitants possessed neutralizing antibodies.