The polymerase chain reaction (PCR) was used to detect human herpes virus 6 (HHV-6) sequences in tissue culture. A pair of primers was synthesized and used to amplify a conserved region of the genome. Amplified products were detected either by visualization of UV illuminated ethidium bromide stained gel or, by hybridization with a specific radiolabeled oligonucleotide. As little as 5 fg of HHV-6 could be detected in infected cells, making this assay suitable for diagnostic purposes.