In nitroglycol workers in an explosives factory, the mean of the specific gravity of their whole blood was found to be nearly at the lowest margin of the physiologically distributed values. Even after improvements in the environmental conditions and enforced health supervision, the recovery was not yet satisfactory. Even in workers working in the place where the concentration of nitroglycol wasat about the threshold limit, the decrease of the blood specific gravity was noticed. This fact must be considered in regards the threshold limit as to chronic poisoning.