In a previously described outbreak of epidemic myalgia, in which Coxsackie virus (Dalldorf's type B 3) was recovered from about one third of the cases, there were a large number of patients with aseptic meningoencephalitis. Virus was recovered from the fluid of one of these patients. One of the strains isolated from the patient gave rise to infections of four laboratory workers, three with the clinical diagnosis of epidemic myalgia and one with meningo-encephalitis. In one of the patients with epidemic myalgia, who had a double infection with both A and B strains, there were vesicles in the posterior portion of the pharynx suggestive of herpangina. The same A-type (Dalldorf's type A 4) was isolated from a laboratory worker with symptoms of “minor illness”. In all cases a rise in neutralizing antibodies to the isolated strain was demonstrable. In experiments on two seriously malformed children orally infected with the above-mentioned B-strain the recurring fever typical of epidemic myalgia was with all probability reproduced. In another case only a sub-clinical infection was obtained. On the basis of these observations the author discusses the etiological role of Coxsackie virus in different syndromes.