Lectins are carbohydrate-binding proteins of non-immune origin that can be assayed as agglutinins. They are potential mediators in recognitive processes and cell adhesion by interaction with glycoconjugates. These functions are areas of particular relevance to tumor growth and metastatic spread. The presence of lectins in tumors has first been inferred by histochemical and cytological methods. The biochemical analysis for lectins with various specificities reveals differences in the lectin profile between tumors of different classes (eg, mammary adenocarcinoma, rhabdomyosarcoma, or teratoma) and of the same class (eg, testicular germ cell tumors) and differences in relation to normal tissues. The presence of endogenous lectins in tumors, their relation to lectins of normal tissues, and their interaction with glycoconjugates of tumors and normal tissues may contribute to an understanding of intercellular interactions during the complex process of metastatic spread, and may allow to establish a new tool for diagnosis and a lectin-based therapy.