In Japan and the United States, where vaccination against varicella-zoster virus (VZV) infection with the live attenuated Oka strain of varicella is routine, cases of chickenpox or shingles occurring in vaccinees can be caused by either wild-type or vaccine virus. Differentiating such cases is important epidemiologically and can be achieved only using molecular typing methods. In the United Kingdom, the Oka vaccine is being considered for use in groups at risk of severe primary varicella, such as seronegative immunocompromised patients and women who may be considering pregnancy. In addition, seronegative health workers who may be occupationally exposed to VZV infection might also be offered vaccination. We analysed 249 U.K. wild-type VZV strains, 105 from cases of chickenpox and 144 from shingles cases, to determine whether they could be distinguished from Oka by the genotyping systems used in Japan and the United States. Four polymorphic loci were examined, a Pst 1 restriction site in gene 38, a Bgl 1 restriction site in gene 54, the R5 repeat region, and the R2 repeat region. The results suggest that U.K. strains of VZV are more similar to U.S. strains than to Japanese strains. All the U.K. wild-type viruses were positive for the Pst 1-1 restriction site, unlike Oka, which is negative. However, one of thirty strains was indistinguishable from Oka at all other loci.