AIM: To assess prevalence of autoantibodies against beta(1)-adrenoreceptors (beta(1)-AR) in patients with arrhythmias of various etiology. MATERIAL: Patients with arrhythmias (n=110, including 59 patients with primary [idiopathic] electrical abnormalities, 33 - with chronic myocarditis and dilated cardiomyopathy [DCM]; 18 - with ischemic heart disease [IHD]) and healthy control subjects (n=20). METHODS: Antibodies against beta(1)-AR were measured in blood serum by direct immunoassay. Synthetic fragment containing 26 amino acids of beta(1)-AR second loop was used as antigen. RESULTS: Patients with primary electrical abnormalities and chronic myocarditis/DCM had similar prevalence of beta(1)-AR (49.1% and 54.5%, respectively), what was significantly higher than in controls (10%) and in patients with IHD (16.6%). These results provided evidence for the possible presence of an autoimmune process in the genesis of idiopathic arrhythmias. Among patients with idiopathic arrhythmias beta(1)-AR were found in 40% (10 of 25) of patients with ventricular tachycardia (VT), 63.6% (14 of 22) of patients with ventricular extrasystoles (VE), 41.6% (5 of 12) of patients with atrial fibrillation (AF). Among patients with chronic myocarditis and DCM beta(1)-AR were found in 72.2% (13 of 18) of patients with VT, 28.5% (2 of 7) of patients with VE, 37.5% (3 of 8) of patients with AF. Among patients with idiopathic arrhythmias female sex and frequent respiratory viral diseases were more common in beta(1)-AR-positive compared with beta(1)-AR-negative patients. VT and left ventricular ejection fraction <40% were more common in beta(1)-AR-positive than beta(1)-AR-negative patients among those with chronic myocarditis and DCM.