1. A system for controlling the exchange of information between an insurer and multiple health care providers in a health care delivery system, where each health care provider has an associated subgroup of subscribers from a group of subscribers within the insurer's health plan, the system comprising: an insurer computer configured to maintain an insurer database of subscriber insurance data on the group of the insurer's subscribers, the database having a first predetermined format; an information-exchange computer operatively connected to the insurer computer to receive at least some subscriber insurance data on the group of the insurer's subscribers therefrom, the information-exchange computer being configured to store that subscriber insurance data in an exchange database in a second predetermined format that is different from the first predetermined format; and plural provider interface computers located at plural corresponding health care providers offices, each provider interface computer being operatively connected to the information-exchange computer to receive therefrom and store in a provider database subscriber insurance data for the subgroup of subscribers associated with the provider, where changes in subscriber insurance data for each subgroup stored in the insurer computer are automatically transmitted to the information-exchange computer and then forwarded to the provider interface computer corresponding to the provider with whom the subgroup is associated, to thereby automatically maintain the currency of the provider database as the subscriber insurance data changes.