The purpose of this study was to find out whether transesophageal pacing could be utilized for assessment of sinus node function, besides Wenckebach point, in patients with sick sinus syndrome. In 17 patients with sino-atrial disease (group I) we compared the results of sinus node tests obtained both in the basal state and after pharmacological autonomic blockade by endocavitary stimulation and 24 hours later, by transesophageal pacing. In another group of 17 patients with sino-atrial disease (control group) we compared the results obtained from two endocavitary studies. In group I, sinus cycle length and corrected sinus recovery time did not show significant differences between the two studies either the basal state or after autonomic blockade, whereas sino-atrial conduction time was more prolonged during esophageal pacing (P less than 0.01). In the control group, sinus node measures did not show significant differences between the two studies. In group I, the following coefficients of correlation were obtained: A) in the basal state sinus cycle length, r = 0.65, corrected sinus recovery time, r = 0.57, sinoatrial conduction time, r = 0.52; B) after autonomic blockade sinus cycle length, r = 0.95, corrected sinus recovery time, r = 0.62 and sino-atrial conduction time, r = 0.53. In the basal state, the correlation for sinus cycle length and corrected sinus recovery time between the two studies was lower in the "study group" than in the "control group" (P less than 0.05). However, after autonomic blockade the correlation for sinus node measures did not show any significant differences between the two groups of patients.(ABSTRACT TRUNCATED AT 250 WORDS)