OUTLINE: Patients receive iodine I 131 humanized monoclonal antibody A33 (131I-huAb A33) by IV infusion over 20 minutes every 6-8 days for up to 8 weeks (depending on dosage). Patients receive a minimum of 6 weeks of treatments. In the absence of disease progression or unacceptable toxicity, patients are retreated no sooner than 6 weeks after the previous course. Cohorts of 3-6 patients receive escalating doses of 131I-huAb A33 to determine the maximum tolerated dose (MTD). The MTD is defined as the highest dose at which no more than 2 of 6 patients experience dose limiting toxicity. Patients are followed for 6 weeks after the last treatment.