To clarify the relationship between in the increase in subcutaneous tissue perfusion rate (TPR) upon inhalation of radon water and the vasoactive effects of radon, rabbits inhaled nebulized water containing 14,000-18,000 Bq/1 radon (radon group) taken from Ikeda Mineral Spring, Shimane Pref., Japan. Control rabbits inhaled radon water from the same springs which had been kept for over 10 radon half-life periods. TPR was evaluated 15 minutes after the beginning of inhalation by mass spectrometry. After inhalation for 90 minutes, plasma and adrenal glands were removed, and levels of adrenaline and noradrenaline were analyzed by high-performance liquid chromatography (THI mithod). Each group was divided into 4 subgroups according to intravenously injected medication as follows : 1) no medication (without adrenergic blocker), 2) phentolamine (α-blocker), 0.05mg/kg/min, 3) propranolol (non-selective β-blocker), 1mg/kg, and 4) atenolol (selective β1-blocker), 6mg/kg. In the radon group, plasma adrenaline and noradrenaline levels were significantly higher (p<0.01, p<0.05), and adrenaline and noradrenaline levels were significantly lower (p<0.01, P<0.01), than those in the control group. In the no medication and phentolamine subgroups, TPRs in the radon group were significantly higher than those in the control group (p<0.01, P<0.01). In the propranolol and atenolol subgroups, no significant change of TPR was found. It is suggested that catecholamines are secreted from the adrenal glands upon inhalation of radon water and that the β1-action of catecholamines contributes to the increase in tissue perfusion.