The frequency of cardiac conduction disturbance in ankylosing spondylitis is discussed. Risk of such disturbance in the patients' relatives is, to our knowledge, not known. To examine these problems, ECG records of 99 patients with ankylosing spondylitis and 132 of their adult first degree relatives were obtained. P-R intervals were determined by standardized methods and compared with P-R intervals of the controls. The distribution of P-R intervals both in the patients and their relatives was close to the controls'. Four cases of first degree AV block were found among the patients (P-R intervals 0.21-0.26 sec), one of them had aortic valve insufficiency. The single case of pronounced conduction delay (P-R interval 0.42 sec) was recorded in an otherwise healthy HLA B27-positive relative. One male secondary case of ankylosing spondylitis had a P-R interval of 0.22 sec. Patients who had experienced acute anterior uveitis had relatively long P-R intervals, while patients with psoriasis had relatively short P-R intervals. The conclusion was that cardiac conduction disturbance was not frequent in patients with ankylosing spondylitis or in their relatives.