The prevalence of diabetes was investigated in 473 patients who had been fitted with pacemakers because of severe bradycardiac arrhythmia. Irrespective of the type of arrhythmia, 36.1% of the male and 45.5% of the female patients exhibited overt diabetes. The metabolic disorder was known in about half (55%) of the cases; average duration of known diabetes in these patients was 7.1 years (0.5-23 years). The more frequent occurence of diabetes in women was attributed to the frequency of overweight (twice as high) in this group. Only one fifth of the male and one tenth of the female patients had myocardial infarction as a sign of manifest coronary arteriosclerosis. The 6 to 10 times higher diabetes prevalence of pacemaker patients compared to the general population of corresponding age may indicate ischemic damage to the conduction system caused by diabetes-specific vascular changes.