 Patients receive iodine I 131 metaiodobenzylguanidine IV over 2 hours. Beginning 10 days later, patients with low neutrophil counts receive filgrastim G-CSF subcutaneously until blood count recovers. Patients with stable or responding disease may receive a second dose of iodine I 131 metaiodobenzylguanidine at least 6 weeks after the first dose. 