The visna-maedi virus was immunologically diagnosed using an immunoblotting technique from an antigenic preparation of the visna-maedi virus K796 purified by sucrose density gradient centrifugation. After SDS-PAGE electrophoresis and transfer onto a nitrocellulose sheet, the immunoblotting procedure was adapted to the search for specific antibodies in ovine serum samples. The results obtained showed that, in the natural visna-maedi disease, antibodies are not systematically detectable against every viral protein of the virus core. We have demonstrated the existence of antibodies directed against the proteins coded by the gag and the pol genes.