To establish the usefulness of Ajmaline test for the evaluation of sinus node function, 77 pts (47 M, 30 F, mean age +/- SD = 61 +/- 15 yrs) first underwent an electrophysiologic study and then were followed-up for a mean period of 46.3 months. The following parameters were determined before and after i.v. administration of Ajmaline (1 mg/kg in 1 minute): sinus cycle length (SCL), corrected sinus node recovery time (CSNRT) and sino-atrial conduction time (SACT). The pts were divided into 3 groups: Group A: 10 pts without clinical or electrocardiographic signs of sinus node dysfunction (SND) and with normal control CSNRT and SACT (less than or equal to 500 and less than or equal to 120 msec, respectively); Group B: 46 pts with clinical-electrocardiographic signs of suspected or apparently not severe SND (sinus bradycardia greater than or equal to 40 beats/min and/or syncopes with positive vagal manoeuvres) and/or slightly abnormal control CSNRT (greater than 500 less than or equal to 600 msec) and/or SACT (greater than 120 less than or equal to 150 msec); Group C: 21 pts with clinical-electrocardiographic signs of apparently severe SND (sinus bradycardia less than or equal to 39 beats/min, sino-atrial block, sinus arrest) and/or definitely prolonged control CSNRT and/or SACT (greater than 600 and greater than 150 msec, respectively). The Ajmaline test was considered negative for the presence of a severe SND if SCL was not prolonged after the administration of the drug more than 20% and CSNRT and SACT were not prolonged more than 50% compared to the control values. Otherwise the Ajmaline test was considered positive. Twenty-seven out of the 77 pts studied underwent permanent pacemaker implantation (23 immediately after the electrophysiologic study and 4 during the follow-up). The following results were obtained: the Ajmaline test was negative in 100% of group A, 87% of group B and 48% of group C pts and positive in 0% of group A, 13% of group B and 52% of group C pts; during the follow-up a negative test resulted predictive in 56 out of 60 pts (92%) and a positive test in 16 out of 17 pts (94%). The predictive accuracy of the test was, therefore, 93.5%. These results indicate that Ajmaline test is an useful provocative test for disclosing, during electrophysiologic studies, pts who have severe SND and for selecting those who need pacemaker implantation.