Two cases are presented of replication of enteroviruses over a long period of time, that caused a protracted atypical clinical course of infection. No typical clinical markers of infection can be seen in the wake of enterovirus replication; the replication itself can be of a protracted recurrent character. Replication of enteroviruses is capable of inducing a protracted recurrent subfebrile condition in adults that has no clinical signs of immunodeficiency state. Parallel activation of replication of a number of viruses, according to our data, is a widespread phenomenon, which fact is to be taken account of in planning examination and treatment strategies. Laboratory tests are needed for the activation of diseases of enteroviral etiology to be ascertained.