Medical Markup Language (MML), as a set of standards, has been developed over the last 8 years to allow the exchange of medical data between different medical information providers. MML Version 2.21 used XML as a metalanguage and was announced in 1999. In 2001, MML was updated to Version 2.3, which contained 12 modules. The latest version--Version 3.0--is based on the HL7 Clinical Document Architecture (CDA). During the development of this new version, the structure of MML Version 2.3 was analyzed, subdivided into several categories, and redefined so the information defined in MML could be described in HL7 CDA Level One. As a result of this development, it has become possible to exchange MML Version 3.0 medical documents via HL7 messages.