Retrovirus-related DNA sequences have been cloned from human DNA and characterized by comparing their nucleotide sequences with the published sequence of Moloney murine leukemia virus (MoLV). One set of clones represents a retrovirus which infected the common ancestor of man and chimpanzee. A second set of clones contains sequences with homology to both gag and pol genes of MoLV and is present as a family of related but not identical sequences are very distantly related, the regenome. Since the two sets of sequences are very distantly related, the results suggest that human DNA contains a number of families of integrated retroviral genomes.