Glycosylation represents 50% of the molecular mass of the human immunodeficiency virus mature envelope glycoproteins (Env), The functional significance of this unusually high level of glycosylation has been partially clarified through a variety of experimental approaches and this has resulted in a demonstrable role. for glycans in posttranslational events, including efficient intracellular routing and the functional folding of the molecule. Alteration of Env glycosylation may, therefore, modulate biological activity and offers the possibility of reducing virus pathogenicity; indeed, removal of glycosylation sites or alteration of the pattern of glycosylation by drug treatment have both been shown to lead to impaired virus infectivity. As a target for antiviral therapy based on the alteration of glycosylation, therefore, HIV Env represents an attractive target.