Lectin cytochemistry of the human autopsy cases of Creutzfeldt-Jakob disease and old cerebral infarction was performed on formalin-fixed, paraffin-embedded sections using 15 lectins. Reactive astrocytes showed a positive reaction with concanavalin A (Con A), Lens culinaris agglutinin (LCA) and Pisum sativum agglutinin (PSA), with common specificity for both mannose and glucose. However normal astrocytes demonstrated no or little cytochemical reaction for any of the lectins. Reactivity for the lectins in control sections was obviously reduced using the blocking sugars (0.1 mol/l D-mannose and 0.5 mol/l D-glucose for Con A, LCA, and PSA, and 0.5 M mol/l alpha-methyl mannopyranoside for Con A). The present data provide suggestive evidence that the reactivity for Con A, LCA, and PSA is increased in reactive astrocytes.