Ten beagles were exposed by inhalation to aerosols of ${}^{90}{\rm Y}$ in fused clay particles to study the radiation dose to the gastrointestinal (GI) tract and effects resulting from clearance of the upper respiratory tract after the deposition of high initial body burdens of inhaled ${}^{90}{\rm Y}$. Focal colonic lesions were found in two dogs, 8 and 12 days after inhalation of ${}^{90}{\rm Y}$ that resulted in GI burdens (GIB) of 18 and 34 mCi. Similar, but less severe, lesions were found in two dogs sacrificed 27 days after exposure with GIBs of 18 and 32 mCi. No GI lesions were found in six dogs with GIBs of 9-18 mCi. Two of the 10 dogs had thermoluminescent dosimeters surgically implanted in the GI tract lumen and submucosa. The highest radiation doses were measured in the colon. One dog, with measured doses to the colon of 3200-5700 rads, had focal colitis when sacrificed 8 days after exposure. The other dog, with doses to colon of 1000-2800 rads had no GI lesions at sacrifice 8 days after exposu...