Head upright tilt table testing is a promising technique for the evaluation and management of vasovagal (neuroregulatory) syncope. In order to determine the day-to-day reproducibility of results using this technique we performed head upright tilt table testing (with or without graded isoproterenol infusion) in 21 patients (12 males, 9 females, mean age 34 +/- 19.1 years). During the first tilt study a total of 14 patients experienced syncope (six during baseline tilt, mean tilt time 15.8 +/- 7 minutes, eight following tilt with graded isoproterenol infusion, mean tilt time 17.7 +/- 9 minutes) while seven were negative. During the second tilt study (performed 3-7 days following the first study) the results of the first study were duplicated in 19 patients (90%) (six during baseline tilt, mean time 17.5 +/- 8 minutes, eight following graded isoproterenol infusion, mean time 15.9 +/- 7 minutes), however the level of provocation required to provoke syncope differed from that needed in the initial test in five patients (24%). We conclude that the results of head upright tilt table testing with graded isoproterenol infusions can be duplicated in 90% of patients, although some day-to-day variability exists in the degree of provocation necessary to elicit a positive response.