Exercise and pharmacologic tests were used for evaluation of the sinus node and S-A function. In all 10 normal persons, the heart rate raised above 90/min without development of cardiac arrhythmia. Among 13 patients with sinus node failure, only 1 had the heart rate raised to 90/min after exercise test and 7 above 90/min after medicinal induction. Cardiac arrhythmia, which is characteristic in sinus node failure, may appear during the test, provide an important clue in making a diagnosis. Criteria for the provocative tests are described. During the test, it is necessary to be on guard against any untoward effects. The patients in this study have been all uneventful throughout.