We have generated amphotropic and Gibbon ape leukemia (GaLV) viruses carrying either a full-length (IG-GC2) or a shortened glucocerebrosidase cDNA (IG-GC4). For all recombinant retroviruses, a single infection was sufficient to augment glucocerebrosidase activity in unselected Gaucher type I and type II fibroblasts to levels which can be considered therapeutic. Transfer efficiency of the glucocerebrosidase cDNA into normal human and Gaucher type I CD34+ cells, using supernatant transduction, ranged from 4 to 50% as established on vector-positive CFU-GM. In these experiments, GaLV and amphotropic virus were equally efficient in transducing early human progenitors. Importantly, mixing amphotropic and GaLV pseudotyped retroviruses resulted in significantly higher transduction efficiencies as compared with single infections, up to 70% vector-positive CFU-GM. Glucocerebrosidase activity, measured in the progeny of human CD34+ cells, increased up to 460% compared with mock-infected CD34+ cells. Upon transduction of Gaucher CD34+ bone marrow cells the glucocerebrosidase deficiency was reversed.