Molecular analysis of the LMP (latent membrane protein) oncogene was performed in 21 Epstein-Barr virus (EBV) positive cases of Hodgkin's disease (HD) with proven LMP gene expression. In each case, viral DNA of the LMP gene was assessed for polymorphism (deletions, insertions, mutations) by polymerase chain reaction (PCR) amplification with selected primers. Specificity of the amplified targets was proven by internal oligonucleotide hybridisation and nested primer PCR. Homogeneity of the 5' LMP gene region coding for the amino terminal, transmembrane, and short extracytoplasmic domains of the protein was identified in all cases. However, deletions or insertions of small DNA sequences within the coding region for the intracytoplasmic LMP domain were observed in about 20% of cases. In one of them, a 30-base-pair deletion was precisely localized by DNA sequencing. A particularly high frequency of DNA polymorphism (30% of cases) was found in the 3' untranslated LMP region. However, when analysing the LMP gene in seven benign conditions, no DNA polymorphism was found. These data suggest conservation of oncogenic LMP regions coding for the protein domains known to be associated with transforming capacities and immunogenic functions. They also show a considerable genomic heterogeneity of the coding region for the intracytoplasmic domain and the 3' untranslated mRNA region. This LMP DNA polymorphism identified within a localized (Swiss) population suffering from HD is unexpected. Its eventual clinical significance remains to be determined.