In infantile lysosomal storage disease associated with osteopetrosis the nature of the enzyme deficiency as well as the type of material accumulated are both unknown. We used lectin histochemistry to characterize the storage material of previously reported cases. Using paraffin sections neurons stained positively with Luxol fast blue (LFB), periodic acid-Schiff (PAS), Concanavalia ensiformis agglutinin, Datura stramonium agglutinin, Griffonia simplicifolia-I, Lens culinaris agglutinin, Ricinus communis agglutinin-I, succinylated wheat germ agglutinin and wheat germ agglutinin, indicating an accumulation of fucosylated N-glycosidically linked oligosaccharides containing beta- and alpha-galactosyl residues and compounds containing N-acetyllactosamine. Reticuloendothelial cells in liver and in spleen did not stain with LFB, but did stain with PAS and the above lectins. These results indicate that there is storage of both carbohydrates and lipids in neurons, and stored carbohydrates with similar residues in reticuloendothelial cells in this disease, where the primary defect is still unknown.