The shedding of 2 tumor-specific glycoprotein antigens from human melanoma cells into spent culture medium was selectively inhibited by nontoxic doses (0.5 microgram/ml) of tunicamycin, an inhibitor of N-asparagine-linked glycosylation. The inhibition of shedding of these 2 antigens with m.w. of 240K and 94K is complete within 24 hr after addition of tunicamycin. During this time interval, our data suggest that these glycosylated cell surface antigens are replaced by their nonglycosylated forms. Removal of tunicamycin or addition of N-acetyl glucosamine restores shedding of these melanoma-associated antigens with initially reduced glycosylation. This same selective inhibition of shedding was observed with cultures adapted to grow in high doses (2.5 microgram/ml) of tunicamycin that otherwise killed > 98% of the cells upon first exposure. In contrast to other glycoproteins found in spent culture medium of melanoma cells, the shedding of melanoma-associated antigens is strictly dependent on glycosylation.