Two infants are described, who, we suggest, represent a fourth subtype of carbohydrate-deficient glycoprotein (CDG) syndrome. Both patients showed microcephaly and severe epilepsy with absent psychomotor development and similar minor dysmorphic features. There were no signs of liver dysfunction. Several glycoproteins in blood, including transferrin, α1-antitrypsin, antithrombin and thyroxine-binding globulin, demonstrated abnormal isoforms suggesting a partial deficiency of mainly one or two sialic acid residues. Both the clinical picture and the glycoprotein abnormalities were different from previously defined types of CDG syndrome.