We studied 41 patients (21 m, 20 f) aged 22-70 years (mean 51) with syncope of unexplained origin using 60 degrees head-up tilt test (TT). Continuous ecg recording and direct arterial blood pressure were monitored. In case of positive response (e.g. syncope) in first examination next TT after administration of atropine (0.02 mg/kg) was performed. In first TT syncope was evoked in 19 patients (46%). Mean time from onset of tilt to syncope (TOS) was 15 +/- 13 min. Atropine administration protected against syncope during second TT in 7 patients, prolonged TOS in 4 (from 12 +/- 7 to 34 +/- 4 min) and shorted TOS (from 26 + 17 to 16 + 14 min) in the next 8 patients. We distinguished on that base: in 7 patients cardioinhibitory form, in 4 mixed form and in the next 8 patients vasodepressor form of vasovagal syndrome. We used in treatment: a) implantation of DDD or VVI pacemaker in 7 patients, b) clonidine in 8 patients, c) propranolol in 2 patients, d) derivates of atropine in 2 patients. During 1 year follow-up 14 patients are free of syncope and in the next 5 syncope occurred rarely. CONCLUSIONS 1. Head up tilt test is very useful in diagnosis of syncope of unknown origin. 2. Second tilt after administration of atropine in patients with syncopal response in the first test helps to differ the type of vasovagal syndrome and to improve its treatment.