Neuroblastoma is among the most common malignancies of childhood. Despite greatly improved therapy for some pediatric tumors, the prognosis for children with metastatic neuroblastoma has not changed significantly in the past 10 years. With conventional chemotherapy, radiation therapy, and surgery, children with metastatic neuroblastoma have a 20% long-term survival rate. We have pursued novel chemotherapeutic approaches to neuroblastoma that target the neurotransmitter receptors on the surface of these cells. Specificity for these neural crest tumor cells is effected by (1) selective protection of normal neuronal elements from toxicity, or (2) selective potentiation of toxicity for neural tumor cells. In the first instance, the oxygen radical-generating neurotransmitter analogue 6-hydroxydopamine is used as a neural crest-specific toxin. Normal neural crest cells are protected from this toxicity by oxygen radical-scavenging analogues of the compound WR2721, which is specifically taken up by nonneoplastic cells. In the second instance, neocarzinostatin, an antineoplastic natural product that must be activated by thiol groups to be toxic, is used in conjunction with 6-mercaptodopamine, a thiol-containing compound that gains specific entry into neural crest cells by virtue of its neurotransmitter-like structure. We have found that neocarzinostatin induces morphologic differentiation of neuroblastoma cells, and we are also currently characterizing the biochemical accompaniments of this morphologic change.