In previous studies a novel lectin-like glycoprotein was isolated from silkworm faeces and shown to recognize sugar chains, especially mannose on the cell surface as an epitope, and to cause aggregation of various types of cells in suspension. However, this substance caused detachment and aggregation of only some types of plated cells, such as QM-RSV cells, which are quail myoblasts transformed with a temperature-sensitive mutant of Rous sarcoma virus (ts-RSV) at 35.5 °C, a permissive temperature for RSV. As described here, during studies on the mechanism of cell detachment and aggregation of QM-RSV cells by this new lectin, some novel biological activities of the lectin were recognized. This lectin was found to bind to immunoglobulins (Ig) specifically at specific amino acid sequences, not via recognition of their molecular conformation. It also recognized the neural cell adhesion molecule (NCAM), which is one of the members of the Ig-superfamily that have Ig-like domains. Furthermore, it had a strong mitogenic effect on lymphocytes, and also caused about 3-fold of phagocytosis by macrophages within 24 hr after its addition.