'MI-Labeled L-fucose-albumin complex and rat preputial fi-glucuronidase are rapidly cleared from plasma after intravenous infusion. L-Fucose-albumin retards the plasma clearance of fi-glucuronidase whereas D-fucose-albumin is inactive. In vitro, '5I-labeled L-fucose-albumin is taken up into rat or rabbit alveolar macrophages by receptor-mediated pinocytosis. Uptake (37°C) is time-dependent, is saturable with increasing ligand concentration (KY e = 4.4 X 10-8M), and requires Ca2". i25ILabeled D-fucose-abumin is poorly taken up. Binding (4°C) is saturable and Ca2+ dependent. Binding and uptake are fully inhibited by yeast mannan. A series of neoglycoproteins, including Lfucose-albumin, were tested as inhibitors of uptake of '25I-labeled 3-glucuronidase into macrophages. The following order of potency was observed:L-Fucose-terminated oligosaccharides coupled to bovine serum albumin also block`5I-labeled (3-glucuronidase uptake into macrophages.