Abstract The aim of the study was to determine interobserver variation in the interpretation of the course of serum enzyme concentration changes in suspected acute myocardial infarction. The study was performed retrospectively and had no relation to the treatment of the patients. In 107 patients, two specialists in cardiology, two specialists in internal medicine, and two trainees, independently evaluated courses of enzyme concentrations and decided whether they were suggestive of acute myocardial infarction. Frequency of positive assessments varied for the six observers from 33 to 53% ( P < 0.01). Pairwise comparison of observers showed a median agreement rate of 0.90 (range 0.78 to 0.96). After adjusting for chance agreement a median kappa value of 0.79 (range 0.56–0.92), was achieved. No difference was found in level of agreement between specialists and trainees. Interobserver variation is an important consideration in the interpretation of the course of serum enzyme concentrations and may have an extensive impact on the final diagnosis of acute myocardial infarction.