Herpes simplex virus subtype 1 deoxyribonucleic acid (DNA) was sheared in a French press to uniform fragments, denatured by heating, then allowed to reassociate. The renaturation reaction followed second-order kinetics with a single rate constant indicating that at least 95% of the genome was unique and that repetitive sequences, if present, were not detectable by this technique. The kinetic complexity of the herpes simplex genome was determined by DNA renaturation kinetics to be (95 +/- 1) x 10(6) daltons. Since this value is in excellent agreement with the molecular weight of viral DNA [(99 +/- 5) x 10(6) daltons] obtained from velocity sedimentation studies, it is concluded that virions contain only one species of double-stranded DNA molecules 95 x 10(6) to 99 x 10(6) daltons in molecular weight.