Human cytomegalovirus (HCMV) cloned EcoRI fragments R and b hybridized strongly, under standard high-stringency conditions, to uninfected cellular DNA of human, murine, or sea urchin origin. Less hybridization was detected with fragments, A, C, E, WL(F), WN(H), I, M, O, P, Q, V, c, d, and e. Southern blot analysis of the HCMV-related human DNA localized the major sites of hybridization of HCMV EcoRI fragments R, b, and d to defined regions of the 28S rRNA gene.