Lectin histochemical studies were performed on selected formalin-fixed, paraffin-embedded tissues of patients affected with the O variant of GM2-gangliosidosis (i.e., Sandhoff's disease). The purpose was to identify specific sugar residues of undegraded "stored" substances in cytoplasm of affected cells. We studied neural tissues from 13 patients, visceral tissues from four patients, and placentae from three affected fetuses. Neurons in all 13 cases studied stained with Concanavalia ensiformis agglutinin (Con A) and with Ulex europaeus agglutinin-I (UEA-I). Succinylated wheat germ agglutinin (S-WGA) stained affected visceral cells and astrocytes and macrophages in the central nervous system. These results demonstrate that alpha-D-mannosyl and alpha-L-fucosyl residues, which bind Con A and UEA-I, respectively, are present in affected neurons. Furthermore, they revealed the affected non-neuronal cells and astrocytes contain complex carbohydrates with nonreducing terminal beta-N-acetylglucosamine, which binds S-WGA.