for the production of biologicals for parenteral applications have to be tested much more rigorously. ICH Topic Q5A (1997) suggests the following virus tests for different cell banks: 'A master cell bank has to be extensively screened for both endogeneous and non-endogeneous viral contaminants. For heterohybridoma cell lines in which one or more partners are human or non-human primate in origin, tests should be performed in order to detect viruses of human or nonhuman primate origin as viral contaminants arising from these cells may pose a particular hazard. Testing for non-endogeneous viruses should include in vitro and in vivo inoculation tests and any other specific tests, including species-specific tests such as mouse antibody (MAP) test, that are appropriate, based on the passage history of the cell line, to detect possible contaminating viruses.'