The molecular cloning and characterization of a novel human retrovirus, designated lymphadenopathy-associated virus, or LAV, is disclosed. LAV was originally isolated from a patient with acquired immune deficiency syndrome (AIDS). A cloned LAV complementary DNA (cDNA) was used to screen a library of recombinant phages constructed from the genomic DNA of LAV-infected T lymphocytes. The nucleotide sequence of an insert obtained from the recombinant phage clone .lambda.J19 was ascertained through M13 shotgun cloning and the dideoxy chain termination sequencing method. The env coding region was identified and peptides obtained therefrom. These peptides correspond to amino acids 239-294, 273-317, 300-327, 334-381, 397-424, and 466-500 of the LAV env. These peptides provide suitable diagnostic reagents for the detection LAV-specific antibodies and for the generation of LAV-specific immunological reagents.