A novel immunodeficiency virus is disclosed which has the designation MVP-5180/91 and which has been deposited with the European Collection of Animal Cell Cultures (ECACC) under No. V 920 52 318. The characteristic antigens which can be obtained from it and which can be employed for detecting antibodies against retroviruses which are associated with immunodeficiency diseases are also disclosed, as are the DNA and amino acid sequences of the virus.