The electrocardiogram (ECG) is the only means of diagnosing atrial infarction antemortem. Certain ECG changes (PR-segment displacements) have been taken earlier as signs of atrial infarction. The purpose of this study was to assess the interobserver variation on suggested ECG signs of atrial infarction in patients admitted with acute myocardial infarction. The ECGs from 290 patients were evaluated by three physicians with respect to the occurrence of each of the following seven criteria suggestive of atrial infarction: (1) PR-segment elevation > 0.5 mm in lead I; (2) PR-segment depressions > 0.5 mm in leads II and III; (3) PR-segment depressions > 1.2 mm in leads I, II, and III; (4) PR-segment depressions > 0.5 mm in leads V1 and V2; (5) PR-segment elevations > 0.5 mm in leads V5 and V6; (6) PR-segment depressions > 1.5 mm in precordial leads; and (7) abnormal P waves. Kappa values ranged from 0.00-0.86. Of the seven criteria tested only criteria 2, 4, and 7 could be detected in a reasonable number of patients. The interobserver variations of these criteria were considerable, although the strength of agreement could be designated as fair to moderate.