In order to improve the method for obtaining the hypocalcemic proteinous substance precipitated from thymus gland of an ox with calcium chloride, which was found to be unsuitable for purification of the objective protein, fractionation with ammonium sulfate was attempted. The fractions precipitated at the concentrations of 15%, 25%, or 41.7% ammonium sulfate showed a significant effect, showing average decrease of serum calcium level by 10-17% of the initial value upon administrations of 1.0mg/kg body weight in rabbits. The fraction of 15% saturation was obtained in a crystalline-like form. It was also found that the leucocyte activity did not necessarily parallel the calcium activity.
