D-Galactosamine administration to rats (400mg/kg) by intraperitoneal injection induced biochemical alterations in liver plasma membranes. Alterations were studied 4, 16 and 24 h after D-galactosamine injection. Plasma membrane 5’-mononucleotidase activity decreased to 40% of control values. Carbohydrate composition was significantly changed. After 24 h D-galactosamine administration, the diminution in plasma membrane sialic acids and hexoses reached 30% of control values. As detected by SDS-acrylamide gel electrophoresis, high molecular weight glycoproteins of D-galactosamine-treated plasma membranes were modified. Moreover, the incorporation of [35S]-sulfate into membrane glycoproteins decreased after D-galactosamine administration (40–60% of control). The present results show that biochemical alterations in rat liver plasma membranes appear soon after D-galactosamine injection. Marked changes are observed in cell surface glycoproteins, especially in sialoglycoproteins and sulfated glycoprote