THE FIRST ATTEMPT to characterize aseptic meningitis as a distinct entity was made by 'Wallgren (1) in 1925. Although his criteria are still useful today, improved laboratory diagnostic techniques now make it possible to demonstrate that what he originally assumed to be a single disease may occur in the course of infection due to a number of different etiological agents. The enteroviruses, other than the poliovirus, which have been associated with the aseptic meningitis syndrome in epidemic form include ECHO 4,6,9,11,16, and 30 (2), as well as Coxsackie A2, 4, 7, 9, 10, 16, and B1-B6 (3). The other types most frequently implicated, in addition to ECHO 9, are ECHO 4 and Coxsackie B5. The first reported outbreak of aseptic meningitis associated with ECHO 4 occurred in Marshalltown, Iowa, in 1955 (4, 5); the first reported epidemic of aseptic meningitis associated with Coxsackie B5 was in Cerro Gordo County, Iowa, in 1956(6). In a search of the U.S. literature, however, we found no reports of a well-defined epidemic of aseptic meningitis in which two enteroviruses, excluding poliovirus, played major etiological roles. Such an epidemic did occur in Baltimore, Md., in 1967. Baltimoire, in central Maryland, is surrounded by, but is politically distinct from, Baltimore County. According to estimates by the bureau of vital statistics of the Baltimore City Health Department, the population as of July 1, 1966, was 914,000. Approximately 41 percent of the population is nonwhite. Thirty-nine percent of the inhabitants are less than 20 years old. In 1967, epidemiologists of the Maryland State Department of Health, after being notified of an increased number of cases of aseptic meningitis in one Baltimore hospital, undertook a telephone survey of hospitals and offices olf selected pediatricians to assess the possibility of an outbreak in the city. When an increased incidence was confirmed by a number of these sources, letters were sent to all Maryland physicians alerting them to the pattern of symptoms and the laboratory results. Specimens of blood and spinal fluid, stool or rectal swabs, and throat swabs or washings were requested for laboratory study. Most of the reported cases were among the Dr. Garber, Dr. Glick, and Dr. Dupont are epidemic intelligence service officers with the National Communicable Disease Center, Public Health Service. Dr. Garber is assigned to the Maryland State Department of Health in Baltimore, Dr. Glick to NCDC in Atlanta, Ga., and Dr. Dupont to the University of Maryland School of Medicine in Baltimore. Dr. Joseph is assistant director, bureau of laboratories, Maryland State Department of Health, and Mr. Eichler is head of the virus isolation laboratory of that bureau.