A major problem of using red cells as the solid phase in assay systems is the difficulty to bind them strongly to appropriate surfaces. We report here on a number of lectins of different specificities which were examined for their ability to bind red cells to polystyrene 96-well microtitre plates. The use of the Thomsen-Friedenreich antigen-specific lectins, jacalin, mushroom and Maclura pomifera agglutinin proved the most useful for ABO reverse grouping. Jacalin-coated plates were also compared with plates coated with poly-L-lysine and bovine serum albumin/glutaraldehyde for the binding of erythrocyte membranes and were found to be superior. We also describe the colorimetric detection of the solid phase red cell antibody reaction by using an indicator erythrocyte and peroxidase chromogenic substrate.