Yttrium-90 has been described as one of the best radionuclides for tumor therapy when chelated to tumor-associated antibodies. This evaluation is based on the superior properties of this radionuclide (suitable half-life, pure beta-ray emitter of intermediate energy, stable daughter, and suitable chemical properties) and because it is available as a radionuclide generator product by decay of its 28-yr parent 90Sr. We have determined that 90Y obtained from one such generator is suitable for labeling antibodies coupled with DTPA. Furthermore, we have shown that the dissociation rate of [90Y]DTPA-IgG in serum at 37 degrees C is similar to that of [111In]DTPA-IgG at about 8-9%/day. Biodistribution studies of 111In- and 90Y-labeled to DTPA-coupled IgG show that the labels distribute nearly identically at 1 hr postadministration, although differences in distribution are apparent at 24 hr. It is possible that these differences reflect the redistribution of the labels following catabolism at the site of localization.