Neuroblastoma is one of the malignant childhood tumors which have a dismal prognosis, but is known to occasionally mature into benign histology spontaneously. Two cases with either stage III or IV neuroblastoma, whose tumors had not been extirpated at the initial operation, were treated by intra-aortic PGE1 infusion combined with oral papaverine and conventional anti-malignant chemotherapy. This therapeutic modality was effective in one case, where the tumor decreased in size and was removed in a second exploratory operation. The histology of the extirpated tumor was benign ganglioneuroma. In this case, however, distant bone metastases were found after the second operation. The role of PGE1 in the mechanism of bone metastasis remains to be determined.