Human antibody fragments against chrondroitin sulfate proteoglycan 4 can be used to deliver cytotoxic agents to cells which express CSPG4. The agents can be diagnostic or therapeutic moieties. They may be linked by covalent or non-covalent linkages to the antibody fragments. They may be produced as a genetic fusion product or joined together synthetically, for example. When the human antibody fragments are internalized by the cells to which they bind, they can carry with them the attached agents. Thus toxic agents having intracellular targets have enhanced killing upon internalization.
