1. Two soluble arylsulphatases (A and B) have been extracted from ox brain by a modified Albers autolysis method and purified by acetone and ammonium sulphate precipitation and dialysis. 2. A 1600-fold purification was achieved with arylsulphatase A and 320-fold purification with arylsulphatase B. 3. The specific activity of arylsulphatase A was 266000 4-nitrocatechol units/mg. of protein N, and that of arylsulphatase B was 64600units/mg. of protein N. 4. Arylsulphatase A seems to be electrophoretically homogeneous. 5. With 3mm-dipotassium 2-hydroxy-5-nitrophenyl sulphate as substrate the optimum pH for the activity of arylsulphatase A was 4.7, and for arylsulphatase B it was 6.1 with a 60mm solution of the same substrate.
