Three marine invertebrate FITC-labelled lectins, CNL, GCL, and GSL, isolated respectively, from the sponges Chondrilla nucula, Geodia cydonium, and the hexacoral Gerardia savaglia, were used as potential diagnostic tools for different breast tumors. The lectins vary in their carbohydrate binding properties: GSL is D-mannose specific, GCL and CNL D-galactose specific. GSL labels most investigated types of malignant tissues distinctively, while the results with CNL and GCL are less consistent. The well known D-mannose specific lectin, concanavalin A, also binds to tumor tissues, but with much lower intensity than GSL.