BACKGROUND To evaluate the usefulness of the Holter method of sinoatrial conduction time (SACT) calculation in predicting the future occurrence of sinus node disease, and the emergence of indications for permanent pacing in patients with unexplained syncope. METHODS The study group included 218 patients (mean age 55 ± 17 years, 116 men) with syncope of unknown etiology in whom spontaneous atrial premature depolarizations (APDs) occurred during Holter monitoring and SACT could be calculated. A SACT value during daily activity > 150 ms was assumed as abnormal. RESULTS The prospective observation time was 48 ± 11 months. During follow-up sinus node disease was diagnosed in 22 persons, including 18 patients with baseline SACT > 150 ms and 4 with SACT < 150 ms. Indications for pacemaker implantation were found in 16 patients, including 13 patients with baseline SACT > 150 ms and 3 with SACT < 150 ms. In subjects with and without sinus node disease diagnosed during the observation period, baseline SACTvalues were 175 ± 52 ms and 87 ± 34 ms, respectively (p < 0.01), and in patients qualified and not qualified for permanent pacing, the respective values were 178 ± 59 ms and 81 ± 38 ms(p < 0.01). Multivariate Cox analysis showed a significant relationship between baseline SACT > 150 ms and a future diagnosis of sinus node disease and pacemaker implantation. CONCLUSIONS The results suggest that the Holter method of SACT calculation is useful in predicting sinus node disease and indications for permanent pacing in patients with unexplained syncope.