AbstractAs the head‐up tilt test (HUT) is employed to verify the efficacy of undertaking a treatment, we prospectively evaluated the reproducibility of positive and negative results, as well as that of the response type in 64 consecutive patients (mean age 34.6 ± 22.9 years) with syncope of unknown cause. Two HUTs (60 min, 75° ), separated by an interval of 9.77 ± 8.21 days, were performed on each patient. Positive responses were reproduced in the second HUT in 54.5% of the patients. A greater reproducibility (84.3%) was observed for negative responses. Of the 31 patients with a negative first test, 5 had a positive response during the second HUT. Using a multivariate analysis, no clinical variable correlated with the reproducibility of positive or negative results. Likewise, neither arterial pressure nor heart rate observed during the test were correlated with reproducibility. Of 18 patients who reproduced positive responses, 12 (66.6%) did so with the same response modality. In three patients with documented monomorphic sustained ventricular tachycardia, which was hemodynamically well tolerated, and in one patient with temporal spike wave activity in the electroencephalogram, HUT was also positive. It was concluded that the low reproducibility of HUT limits its usefulness as a tool for evaluating treatment efficacy. The variability of the type of response suggests a common mechanism leading to cardioinhibitory and vasodepressor reactions. A positive result in only the second study shows the rationale of performing two tests when the first one is negative.