Abstract: A method of regulating oncogene-mediated cell transformation in a mammalian host. Oncogenes having glycosylated expression products are regulated by administering an effective amount of a processing glucosidase inhibitor: a glucosidase I inhibitor, e.g., castanospermine, N-methyl-1-deoxynojirimycin, 1-deoxynojirimycin, 5-amino-5-deoxy-D-glucopyranose; or a glucosidase II inhibitor, e.g., bromoconduritol. The glucosidase I inhibitors are preferred, particularly castanospermine (CA) and N-methyl-1-deoxynojirimycin (MdN). Oncogenes having glycosylated expression products that are ultimately expressed on the plasma membrane or secreted from transformed cells are particularly susceptible to regulation by these anti-cancer drugs. Also provided is a method of regulating the immune system of a mammalian host. Administration of an effective amount of a processing glucosidase inhibitor suppresses proliferation and differentiation of monocytic and myeloblastic cells.