1. The subcellular distribution of beta-glucuronidase and other hydrolases in rabbit liver was investigated. beta-Glucuronidase was found in both microsomal and lysosomal fractions. 2. Multiple forms of beta-glucuronidase were present in extracts of microsomal and lysosomal fractions. All forms were common to both fractions. 3. A specific antiserum against beta-glucuronidase was raised, and characterized by immunoprecipitation and affinity-chromatography procedures. 4. The immunological identity of the multiple forms in the pure beta-glucuronidase preparation, and the immunological identity of the beta-glucuronidase complement of lysosomal extracts with that of microsomal extracts, were demonstrated by means of the antiserum. The presence of inactive enzyme in various enzyme preparations was shown.