Human herpesvirus 7 (HHV-7) is a lymphotropic virus which replicates in CD4+ T cells. The majority of DNA sequences of HHV-7, strain RK, were cloned, and the termini of the viral DNA inserts were sequenced. The clones were found to contain sequences homologous to HHV-6 DNA with the average relatedness amounting to 60% in the nucleotide sequence and 53.4% in the corresponding amino acid sequences. Human cytomegalovirus (HCMV) DNA was also found homologous but to a lower extent, while the human alpha and gamma herpesviruses were more distinct. Some genes were found to be better conserved in all herpesviruses (core genes). These findings define the genetic makeup of HHV-7 DNA.