In 1985, the European Community set up a 'Concerted Action on Ambulatory Monitoring', whose goal was to define an ECG (electrocardiography) database as a reference for assessing the quality of ambulatory ECG monitoring (AECG) analyzers. Since it is now recognized that ST-T changes are highly relevant for the diagnosis of ischemic heart disease, it was agreed that the project should concentrate on setting up a standard for annotating ST-T changes. The pilot study, completed at the end of 1986, set up a small prototype database. After the project ended, it was decided that the interest shown by research groups and manufacturers warranted developing the full database. Thirteen groups from eight countries agreed to provide AECG tapes and to contribute to the annotations. So far, 106 AECG records, out of 175 submitted, have been admitted to the database and 96 have each been annotated by two different groups. Disagreements between the annotations have been analyzed for estimation of reliability. The first release of the database comprises 50 annotated records stored on CD-ROM. >