Neuroblastoma, the second commonest solid tumor in children, is a neoplasm of the peripheral autonomic nervous system that usually occurs before children are 6 years old. Therapy of localized tumor (clinical stage I and II) and of a special form of metastatic tumor (clinical stage IV-S) is usually successful, but treatment of widespread regional (clinical stage III) or metastatic (clinical stage IV) neuroblastoma is almost uniformly unsuccessful. Unfortunately, two thirds of children have stage III or IV disease at diagnosis. Several clinical trials are in progress. Preclinical investigations with monoclonal antibodies and retinoic acid may lead to new therapies. Monoclonal antibodies that react relatively selectively with neuroblastoma cells may be useful for diagnosis and therapy. Neuroblastoma cells have cytoplasmic retinoic-acid-binding proteins; treatment of cultured cells with retinoic acid induces morphologic maturation and markedly inhibits proliferation.