Soluble antigens of 6 arenaviruses (Tacaribe, Tamiami, LCM, Amapari, Machupo, and Junin) were isolated by gel chromatography in servachromium A-2. It was shown that practically the entire antigenic activity of the original virus-containing preparations in complement-fixation (CFT) and agar gel diffuse precipitation (AGDP) tests was due to the presence of soluble antigens in them. Antigenic relationships of the isolated soluble antigens were studied. Physicochemical characteristics of the soluble antigens were determined: buoyant density in cesium chloride solution, sedimentation properties, and sensitivity to RNase. The experimental results suggest that the soluble antigens are fragments of virion nucleocapsids.