High affinity antibodies were made to gangliosides expressed on tumor cells. The antibodies can be used analytically, diagnostically, therapeutically, and theranostically. The antibodies may be used to target cytotoxic reagents to tumor cells, thus minimizing full-body toxicity. The antibodies may also be used with out added cytotoxin. The antibodies may be detectably labeled or labelable for analytic and diagnostic purposes. The combination of specificity and affinity of the antibodies render them particularly useful.