The unequivocal diagnosis of nonparalytic poliomyelitis is difficult to achieve, since its signs and symptoms are often those associated with aseptic meningoencephalitis, and for this syndrome there may be a variety of causative agents. The most direct evidence of nonparalytic poliomyelitis which can be obtained at present consists in the isolation of the virus from the stools or pharyngeal secretions in suspected cases.1But the isolation of the agent from such sources cannot be regarded as entirely conclusive, and the procedures involved are intricate, time consuming and expensive. They cannot, therefore, be used as routine. The diagnosis, accordingly, is often made on epidemiologic data taken together with the clinical observations. Epidemiologic evidence, however, is intrinsically circumstantial and hence can be considered only as presumptive in character. In contrast to the agent of poliomyelitis, the role of certain other viruses in aseptic meningoencephalitis may be established more easily by laboratory