OUTLINE: This is a dose escalation, multicenter study. Patients undergo octreotide scintigraphy to determine the location of somatostatin receptors. Patients then receive yttrium Y 90-SMT 487 IV over 15 minutes on day 1. Treatment continues every 6 weeks for up to 4 courses in the absence of disease progression or unacceptable toxicity. Cohorts of 3-6 patients each are entered on course I (vertical dose escalation) and courses II, III, and IV (horizontal dose escalation). Cohorts receive escalating doses of yttrium Y 90-SMT 487 until the maximum tolerated dose (MTD) is determined. MTDs are determined for a single course and for 4 courses. The MTD is defined as the dose preceding that at which no more than 2 of 6 patients experience dose limiting toxicities. Results of course I determine the dosage of subsequent courses. Patients are evaluated on days 2 and 7, and at weeks 4 and 6, following each injection of yttrium Y 90-SMT 487. Patients are followed at 12 and 18 months and then annually thereafter.