The polypeptide composition of four Tupaia herpesvirus strains--of which two were isolated from malignant tumors--was analysed by one- and two-dimensional gel analysis. It was found that purified virions of the tree shrew consist of a least 37 viral polypeptides when determined by SDS polyacrylamide gel electrophoresis. The number of viral polypeptides increased to 49 when analysed by the two-dimensional technique with the molecular weights ranging from 12.000 to 230.000. Variations in the viral polypeptide patterns made it possible to differentiate between the different virus isolated even by the one-dimensional method. The two-dimensional technique allows the identification of virus-specific spots among the polypeptides of virus-infected cells. Radiolabeling experiments identified at least five glycoproteins which seem to reside on the surface of the virus envelope. In addition, neutralisation and immunodiffusion tests were performed which revealed cross-reactivities among the tupaia herpesvirus strains. Rabbit anti-tupaia herpesvirus sera did not neutralize other animal or human herpesvirus.