Exposure of vesicular stomatitis (VS) virions to neuraminidase resulted in loss of their ability to agglutinate goose erythrocytes and to attach to L cells concomitant with hydrolysis of sialic acid. These viral adsorptive functions were also destroyed by tryspsinization. Sialyl transferase resialylation in vitro of neuraminidase-treated VS virions restored their hamagglutinating and adsorptive functions almost to original levels. Erythrocyte and L cell receptors for attachment of VS virions were blocked by fully sialylated fetuin and by VS viral sialoglycopeptides. Smaller VS viral glycopeptides generated by extensive trypsinization were less effective inhibitors of hemagglutination than were larger glycopeptides; neuraminic acid and neuraminosyl lactose had no capacity to inhibit hamagglutination or adsorption of virus to L cells. These data suggest that cellular receptors for viral adsorption recognize sialoglycopeptides of a certain size. Neuraminidase desialylation did not significantly alter the isoelectric point of VS virions. Cells exposed to DEAE-dextran, trypsin, or neuraminidase showed significantly increased capacity to attach fully sialylated but not desialylated VS virions. Neuraminidase desialylation of L cells, Chinese hamster ovary cells, and Madin-Darby bovine kidney cells resulted in enhanced susceptibility to plaque formation by VS virus.