['To examine auto-antibodies in the sera of spontaneously hypertensive rats (SHR) and investigate the possibility of abnormalities of the immune system in those rats.', 'Blood samples were taken from 18-month-old SHR and age-matched Wistar-Kyoto (WKY) rats. The immunoglobulin fraction was prepared from the rat sera.', 'Immunoglobulins were investigated in a sensitive biological test system using spontaneously beating neonatal rat heart myocytes.', 'Immunoglobulins prepared from the sera of the 18-month-old SHR increased the beating frequency of cultured rat heart myocytes. This positive chronotropic effect induced by the auto-antibody-containing immunoglobulin fraction was realized via the beta 1-adrenergic receptor.'] Do the sera of spontaneously hypertensive rats contain agonistic auto-antibodies against the beta 1-adrenoceptor?