Abstract: The invention relates to a new variety of retroviruses designated Human Immunodeficiency Virus Type 2 (HIV-2), samples of which have been deposited at CNCM and having Accession Numbers I-502 and I-532. The invention also concerns purified forms of the antigens which can be obtained from this virus, in particular from the gp36 and gp130-140 envelope glycoproteins. These various antigens are useful in medical diagnosis and kits, in particular by being placed in contact with serum of the patient to be diagnosed. The invention further relates to polyclonal and monoclonal antibodies specific for the antigens of HIV-2, particularly antibodies specific for gp130-140 envelope glycoprotein. Lastly, the invention relates to immunizing compositions, in particular containing at least one of glycoproteins gp36 or gp130-140.