A series of man-Chinese hamster somatic cell hybrids with a variable content of human chromosomes was used to study the localization of the human gene coding for the lysosomal enzyme beta-glucocerebrosidase (EC 3.2.1.45). In lysates made from hybrid cells, the human enzyme was specifically recognized by a mouse monoclonal antibody raised against human placental beta-glucocerebrosidase. This monoclonal antibody did not cross-react with Chinese hamster beta-glucocerebrosidase. After reaction of the antibody with the enzyme, beta-glucocerebrosidase was precipitated by addition of Protein A-Sepharose beads, and was detected on the beads by its enzymatic activity. From the analysis of a series of man-Chinese hamster hybrids, among which were hybrids with specific segments of chromosome 1, we conclude that the gene coding for human beta-glucocerebrosidase is localized in the region q21-q31 of chromosome 1.