Seven patients with carcinoma of the lung were studied with radiolabeled B72.3 (In-lll or I-125). Positive scans were obtained in 4 patients. In 2 patients with negative scan immunohistology showed that their tumor did not express the TAG-72 antigen recognized by B72.3. All studies were well tolerated and no side effects were seen. Five patients with colorectal carcinoma have been studied with I-131 B72.3 F(ab')2. Both patients whose tumor expressed the TAG-72 antigen had positive scans while 3 patients with no antigen expression had negative scans. Patient accrual is still in progress.