• Human and primate cells in culture were used to establish viral etiology for aseptic illnesses involving the central nervous system not proved to be poliomyelitis. This program of laboratory studies resulted in recognition and etiological specification of epidemic aseptic meningitis occurring in Minnesota in the summer and autumn of 1956. Tissue culture methods permitted characterization of the epidemic as an outbreak of Coxsackie virus infection restricted, as had not previously been observed, to a single immunotype. This finding provides further evidence that viruses other than the three known types of poliovirus may cause clinical illness designated as nonparalytic poliomyelitis until the causative agent is recovered and identified.