Since August 1960 fatal cases with paroxysm of angina pectoris due to nitroglycol poisoning have been reported. By means of Heines-Brown's cold-pressor tests we have ascertained a relationship between the tone of blood vessels and nitroglycol poisoning. Subjects were workers engaged in press-extending and kneading materials containing nitroglycol. Clerical workers in the same plant were used as controls. Features in common among subjects in question were: Abnormally marked increase of diastolic pressure with little increase of systolic pressure, and decrease of pulsse pressure as a result, during exposure to cold, and delayed arrival of the maximum value of blood pressures. Those who had had paroxysms of angina pectoris showed similar results. Therefore, continued exposure to nitroglycol decreases reactivity to cold stimuli. This fact may be exlained on assuming that elevated vasoconstrictor tone leaves little space for further vasoconstriction by some provoking factors and that this state has been realized in persons exposed to nitroglycol.