The availability of cloned varicella-zoster virus (VZV) DNA probes allows rapid detection of viral-specific DNA by "dot-blot" hybridization in lymphocytes or in lesion aspirates. Thirty-six blood specimens were obtained from 25 patients with suspected varicella or zoster. VZV-specific DNA was demonstrated in 15 lymphocyte preparations of nine patients with varicella and in one with disseminated zoster out of five patients with zoster. VZV-specific DNA was detected prior to rise in antibodies, indicating early viremia in these patients. Virus isolation from lesions and serological tests confirmed VZV infections. VZV-specific DNA was detected in lymphocytes of three patients out of six with active herpetic lesions, whereas it was not detected in lymphocyte specimens from two patients with undiagnosed rash or four with lymphoproliferative diseases, who did not present varicella or zoster, or from 18 healthy controls. No signal was obtained in herpes simplex virus (HSV)-infected and -uninfected cell lines. The hybridization assay proved that specific and viral or cellular DNAs other than VZV did not cross-hybridize with the probe. The sensitivity limit of detection was 4-15 pg of homologous DNA, and the assay was accomplished within 72-96 hr. These results point to the possible rapid diagnosis of VZV infection in patients suspected of varicella or generalized zoster. In addition, simultaneous infection with both VZV and HSV seems to occur in some patients.