MeCO-dried powder (PA), obtained from the supernatant left after separation of the pH 5.4-precipitating fraction from the aqueous extract of bovine parotid gland, was extracted with HOAc.The extract had a hypocalcemic activity in rabbits, but its activity fluctuated.The HOAc extract of the Me2CO-dried powder (PAI) obtained by incubation of a suspension of the sample PA in saline, had nearly constant activity.From the purification of PAI by DEAE-cellulose chromatog. and gel chromatog. on Sephadex G-100, a hypocalcemic protein (P-MSY) was obtained in a yield of 37 mg from 10 kg of fresh gland.The sample P-MSY was homogeneous in disc electrophoresis and electrofocusing and was effective in a dose of 0.01 mg/kg.It has almost the same activity as purified Parotin.P-MSY had a mol. weight of 66,000, isoelec. point of pH 5.60, and sugar content of 2.53%.These properties and the results of amino acid anal. suggest that P-MSY is a hypocalcemic protein differing from purified Parotin.P-MSY was also different from β-Parotin or calcitonin.