Arylsulfatase B (ASB) from lysosomal fraction of rat liver were isolated and purified 260-fold with a recovery of about 5%. 2. The enzyme in gradient PAGE 4-30% followed by immunoelectrophoresis migrated as a single peak of M(r) 84,000. The pI, measured by isoelectrofocusing in agarose followed by immunoelectrophoresis, was equal to 6.7. 3. ASB reacted with Con A, LCA, PSA, LTL, WGA, RCAI and did not react with PHA, SBA, HPA, CAA and PAL in crossed affino-immunoelectrophoresis or rocket immunoelectrophoresis. These results permit of preliminary elucidation of ASB glycan structure.