A human glucocerebrosidase cDNA clone was isolated from a human chronic myelogenous leukemia (line K562) cDNA library using a 36-nucleotide-long synthetic probe (GC-36). The 2.4-kb cDNA contains 184 bp of 5′ nontranslated sequences, the complete coding region, and 546 bp of 3′ nontranslated sequences followed by 100 bp of poly(A). A primer extension experiment indicated that the cDNA is at least 51 bp shorter than the mRNA at the 5′ end. In normal human placenta as well as in fibroblasts from Gaucher's disease patients, a major mRNA species of 2.6 kb hybridizes with the cDNA probe. The amounts of the glucocerebrosidase mRNA in normal placenta and Gaucher's cells are comparable. The cDNA was linked to the SP6 promoter and transcribed in vitro. The resultant RNA, when translated in a cell-free system, yielded a polypeptide of 55 kD, which is the size expected from the coding sequence. The cDNA was inserted into an SV40 shuttle vector, under the transcription control of the SV40 early promoter. COS-M6 cells were transfected with this construct and the biological activity of the cDNA was assayed by monitoring the increase in glucocerebrosidase activity, using 4-methyl umbiliferyl glucopyranoside as a substrate. There was a two- to three-fold increase in enzymatic activity in the transfected cells, compared to nontransfected cells. These results prove the authenticity of the glucocerebrosidase cDNA and provide the basis for experiments to understand the nature of the genetic alterations responsible for Gaucher's disease.