Simian adenovirus SA7 heated for 30 minutes at 70 degrees C retained part of its ability to induce tumors in newborn hamsters. Tumors were also induced by DNA extracted from the heated virus. However, neither residual replicating, i.e. cytopathogenic, nor transforming and T-antigen-inducing activities could be detected in vitro in CV-1 and hamster embryo cells inoculated with the heated virus. The results are discussed in terms of a possible release of viral nucleic acid at the high temperature. They also show that current tests for effective virus inactivation based exclusively on the recognition of replicating virus should be reevaluated.