Plastic-embedded bone marrow biopsies from four patients with Gaucher's disease have been studied histochemically. Concanavalin A (ConA) was found to bind to cytoplasmic inclusions of Gaucher cells; the binding was prevented by lipid extraction or beta-glucosidase digestion. This suggests that glucocerebrosides stored in Gaucher cells are responsible for ConA binding; ConA staining combined with lipid extraction and beta-glucosidase digestion tests may be taken as a tool for the demonstration of Gaucher's cerebrosides of possible practical importance in diagnosis and investigation of Gaucher's disease. An excess of vic-glycol groups with respect to ConA binding-sugar residues and not extractable by lipid solvents are demonstrable in Gaucher cells. Vic-glycols appear to be regularly arranged at the electron microscopy level within Gaucher cell lysosomes along typical Gaucher "tubules", where some kind of interaction between lipid and protein should occur. Acid phosphatase might be one protein species involved in such interaction.