One hundred three patients with persistent sinus bradycardia were evaluated electrophysiologically and followed prospectively for a mean of 4.6 years. The 5-year survival rate was 74.8%, not significantly different from the 72% rate in the general population with similar age and sex distribution. Forty-one patients had abnormal corrected sinus-node recovery time. Overall accuracy of abnormal corrected sinus-node recovery time in predicting serious sinus node disease in symptomatic and asymptomatic patients was 90% (37 of 41 patients) and 100% in patients with syncope (18 of 18 patients). The sensitivity of the test was 66%. Abnormal corrected sinus-node recovery time in patients with sinus bradycardia appears to be a valuable specific, predictive index of serious sinus node disease and therefore a useful test in selecting patients for pacemaker therapy, especially if symptoms such as dizziness or syncope are present.