Immunoscans with the Fab-fragment of the monoclonal anti-myosin antibody R11D10 labeled with 111In showed significant uptake in rhabdomyosarcoma, rhabdoid tumor, and primitive neuroectodermal tumor. The diagnosis of an antimyosin positive or negative tumor with the aid of the immunoscan was superior to clinical findings in combination with ultrasound and CT, and to histological diagnosis in tumor biopsies. In addition chemotherapeutically induced renal impairment can be diagnosed by diminished renal uptake of antimyosin.