Molecular changes occurring in myocardial diseases are not well understood. Proteins, as regulatory molecules, should play an important role in the etiology of these diseases. The method of two-dimensional electrophoresis (2-DE) allows the analysis of some thousand proteins with one experiment. An important prerequisite for this kind of investigation is the possibility of identifying the proteins separated by 2-DE. We resolve 3239 proteins of the human myocardium and tried to identify 33 proteins by amino acid analysis and microsequencing. Twenty proteins were identified by search for the protein-chemical data obtained in the Martinsried Institute Protein Sequence Database. Comparisons of 2-DE patterns of different size, which were obtained in different laboratories, were performed with the result that proteins identified on a 2-DE map of one laboratory can be assigned to spots of 2-DE maps produced by another laboratory. Our results show the usefulness of a myocardial 2-DE database; they can be used in different laboratories and make it possible to generate a collection of important human myocardial proteins in a 2-DE database for comparative studies worldwide.