Monoclonal antibody (MoAb) imaging has contributed greatly to the diagnosis and staging of both colorectal and ovarian cancers, and recently has been tested in patients with prostate cancer. Anatomic imaging modalities such as computed tomography, ultrasound, and magnetic resonance imaging have deficiencies in imaging each of these cancers that can be complemented or overcome by using radioimmunoscintigraphy. The management of patients with colorectal cancer, in particular, has been aided by developments in immunoscintigraphy. The new, safe, and easy-to-prepare MoAbs make possible an effective form of colon and rectal cancer imaging that has been used for (1) staging primary colorectal tumors in presurgical patients, (2) determining extent of disease, (3) continuing surveillance of patients at risk for recurrence of disease, (4) managing patients with elevated carcinoembryonic antigen levels (even those with otherwise negative workup results), and (5) imaging for occult, disease in patients both before and after surgery. In ovarian cancer patients, MoAbs are promising as safe, sensitive imaging tools. The U.S. Food and Drug Administration has approved 111In satumomab pendetide (OncoScint CR/OV; Cytogen Corporation, Princeton, NJ) for use in imaging colorectal and ovarian cancer. Immunoscintigraphy is being refined and tested to locate bony and soft-tissue metastases in patients with prostate cancer. As both a complementary tool and, in some cases, the imaging modality of choice, MoAbs have proven to be safe, accurate imaging tools for many patients with cancer.