To determine if altered infectivity results from inhibitormediated changes in cell surface receptor levels, we measured biotinylated CAT-1 in M. dunni cells transfected with HA-tagged mCAT-1. As shown in Figure 5B , surface mCAT-1 in DMM-treated cells shows the expected reduction in size because of the predominance of smaller highmannose N-glycans, but quantitation of this expression by densitometric scanning shows that the level in DMM treated cells is not significantly different from the untreated control.