An increased prevalence of ankylosing spondylitis and other HLA B27-associated rheumatic diseases has recently been demonstrated in a group of men with permanent pacemaker-treatment. The purpose of the present study was to find out if HLA B27 was associated with severe bradyarrhythmias also in the absence of rheumatic disease. The frequency of B27 was determined in 83 permanently paced men with complete heart block, in whom presence of radiological or clinical signs of a B27-associated rheumatic disease had been excluded. Eighty-four healthy subjects were HLA typed for comparison. HLA B27 was found in 17% of the patients and in 6% of the controls, a significant difference with P = 0.017 (Fisher's exact test). The present study suggests that, in a subgroup of patients with complete heart block, the development of heart block is B27-associated, and that the pathophysiological mechanism is similar to that leading to ankylosing spondylitis. Another B27-associated disease manifestation has been demonstrated.