The polymerase chain reaction (PCR) was used to investigate samples from Indonesian and Swedish patients with cervical intraepithelial neoplasia grade III (CIN III), squamous cell carcinoma or adenocarcinoma of the cervix for the presence of a transforming fragment (BC 24) of herpes simplex virus type 2 (HSV-2) DNA. The PCR test for HSV-2 DNA was more sensitive than the infectivity endpoint titer in a cell culture system and no cross reactivity was found with either varicella-zoster virus, cytomegalovirus, Epstein-Barr virus, human papillomavirus 16 or 18, or human genomic DNA. Using this PCR test, 2 out of 5 cases with CIN III, 10 of 71 squamous cell carcinomas, and 3 of 11 adenocarcinomas of the uterine cervix were found to contain DNA sequences homologous to the BC 24 fragment of the HSV-2 genome. Only two of the samples containing this transforming region of the HSV-2 DNA were positive in a PCR assay for the HSV-2 DNA polymerase gene. The great majority of the HSV-2 BC 24 DNA positive (12 of 15) came from the Indonesian group of patients. All 15 CIN III or cancer samples positive for the HSV-2 BC 24 fragment were also positive for papillomavirus DNA. In line with observations made by others, our data support the hypothesis that HSV infection could represent one of several possible oncogenic cofactors leading to cervical carcinoma. The HSV cofactor might be more important in the Indonesian than in the Swedish population.