A discussion list is a special Internet address that echoes email messages to a list of subscribers. Any standard email system with Internet access may be used to participate in the list. Most discussion lists are limited to a specific topic which in the case of NEUROLIST are topics that are of interest to neurologists. The software that controls the discussion list besides accepting and copying messages, must determine which messages are valid and who may be subscribed to the list. Sophisticated software such as Lyris also will scan for duplicate messages and commands which will cause it to activate special features. Lyris also has a web and newsgroup interface that allows the list to be accessed by the World Wide Web and newsreaders in addition to email. Still, email is the primary method used by most users to access the list. NEUROLIST is a private discussion list, which means that only subscribers who are approved by the list owner may contribute and read messages sent to the list. Other lists may be public, in which case anyone may send a message and join the list. At the other extreme are moderated lists, where all messages must be approved by the list owner.