The aim of this study was to determine both the type of gastric mioelectric and emptying disorders in correlation to degree of severity of hyperthyroidism (clinical and thyroid hormones\' blood levels) and ANS function estimated in HRV analysis. The study was performed on a group of 50 patients (35 with multinodular toxic goitre and 15 with Graves\' disease, 45 females and 5 males, mean age 39.6 years, mean BMI 23.72) with newly diagnosed and so far untreated hyperthyroidism. The control group were 50 healthy volunteers age-, sex-, and BMI-matched to the studied group. Patients were studied twice, within newly diagnosed thyreotoxicosis and after treatment (Metizol) and reaching stable euthyroid state. The study consisted of: a) percutaneous EGG analysis (Synectics): 30 minutes before and after a test meal (ENRICH Liquid 250 ml), b) HRV analysis (ECG POSTER 2002): 10 minutes at rest and during deep breathing test, c) ultrasound measurement of gastric emptying by Bolondi method. Statistical analysis of collected data was performed. In hyperthyroid patients significant both preprandial and postprandial dysrhythmia (33.01% of bradygastria and 16.49% of tachygastria) was found. In some patients decrease of amplitude of EGG signal was marked as a result of antral hypomotility with coexisting significantly prolonged gastric emptying (110 min). Among severe hyperthyroid patients both the antral food distribution (antrum 35% bigger than in a control group) and impaired proximal stomach relaxation were evident. The degree of gastric mioelectric activity and emptying disorders was proportional to the degree of both severity of clinical manifestation of hyperthyroidism in Zgliczynski scale (from I degree to III degrees) and free thyroid hormones\' blood levels (positive correlation). In HRV analysis at rest in hyperthyroid patients comparing to a control group the decrease of both the heart rate variability and a total power was found particularly in HF component resulting in relative sympathetic activation. In HRV analysis during deep breathing test the decrease of heart rate variability was present mostly in LF component. It indicates on reduction of vagal regulation (and vagal excitability) of sinus node and gastric pacemaker function. Coexistence of the increase and decrease of a gastric basic electrical rhythm with delay of gastric emptying indicates on a complex mechanism of their formation. Both neurogenic regulation dysfunction and primary miogenic autoregulation disorders as a result of tyreotoxicosis seem to be the possible causes. All the found changes were functional and disappeared after reaching the stable euthyroid state within 3 months of pharmacological treatment.