In 10 cases of dilated cardiomyopathy the HLA-loci (A, B, C, DR) and marker expression on lymphocytes were studied. In this group the T4/T8-ratio was decreased and interleukin-2-expression was increased in relation to normals or patients with chronic coronary heart disease, respectively. 9 patients had the HLA-A1 or HLA-A2-locus in their siblings. In correlation analysis between immunological and hemodynamic parameters a good correlation of the number of NK-cells to the ejection fraction (r = 0.79) and negative correlation of helpercells (CD4) to the cardiac output were found (r = -0.80). The results of this attempt suggest an immunological pathogenesis of the dilated cardiomyopathy.