Reed-Sternberg cells from ten cases of Hodgkin's disease were examined by the direct immunofluorescence technique, for their affinity for nine lectins. The surrounding lymphocytes and monocytes of HD tissue were also assessed for their ability to bind lectins. RS cells showed considerable heterogeneity of reaction. Overall, there was a marked decrease in the binding of most of the lectins studied in HD cases as compared to normal peripheral blood mononuclear cells. This was particularly evident for RCA, PHA and PNA binding. It is suggested that there is a defect in carbohydrate metabolism, with fewer lectin-binding sites on both RS cells and on the mononuclear cell populations in Hodgkin's disease. Further quantitative work is required to verify this.