The glucosidase removing the outer most glucose residue (glucosidase I) can be inhibited in cell-free assays by N-methyldeoxynojirimycin. In addition, this glucose analog inhibits the very same reaction in intact cells and does not affect the dolichol cycle. N-methyldeoxynojirimycin, at concentration blocking oligosaccharide processing, does not inhibit viral protein synthesis in the infected cells. Furthermore, it does not inhibit exponentially growing human embryo cells and may, therefore, not be very toxic. To investigate whether release of sindbis virus is generally inhibited upon inhibition of formation of complex oligosaccharides, sindbis virus-infected insect cells are used. Insect cells may be unable to make the complex-type of oligosaccharides because some glycosyl-transferases are lacking. Indeed, sindbis virus glycoprotein obtained from infected insect-cells has mainly, if not exclusively, high-mannose-type oligosaccharides.