Since the entity known as aseptic meningitis was described by Wallgren over a quarter of a century ago,1 considerable progress in the recognition of some of the multiple etiologic agents of this syndrome has been made. Wallgren's basic criteria for the diagnosis of aseptic meningitis were: (1) acute onset with obvious signs and symptoms of meningeal involvement; (2) alteration of cerebrospinal fluid typical of meningitis; (3) absence of bacteria in cerebrospinal fluid; (4) relatively short benign course of illness; (5) absence of local parameningeal infection or systemic disease which might present meningitis as a secondary manifestation; (6) absence from the community of epidemic disease of which meningitis is a feature. In general, with the exception of the last named feature, these criteria remain valid. In addition, it should be recognized that the cellular elements of the cerebrospinal fluid are frequently predominantly lymphocytic, although early in the disease there may