SUMMARY.Binding patterns of mouse monoclonal antibodies (mAb) to P1, Pk, N, I, H, Y or A antigens were visualized in the backscatter electron imaging mode of a scanning electron microscope by indirect immunogold labelling. Experiments were performed at room temperature (RT) and at 4°C. In experiments with anti‐P1and anti‐Pk, clusters of immunolabelling particles dominated the immunolabelling pattern much more at RT than at 4°C. By contrast, no clustering was seen with anti‐N, even at RT. Clustering was also observed at RT with anti‐I, anti‐H and anti‐Y, and on some Axand A3cells with anti‐A, but was much reduced at 4°C. Immunolabelling was stronger at 4°C than at RT with all mAb except anti‐N and anti‐A. The results indicate that glycolipid blood group antigens are more mobile in the membrane of intact erythrocytes at RT than at 4°C, and that the cells bind more antibodies to such antigens at 4°C than at RT. We suggest that antigen immobilization in the cold will reduce cross‐linking of antigens and hence increase the number of antibody molecules needed for epitope saturation, leading to increased binding of antibody in the cold. This may be the main reason for cold‐enhanced agglutination with h