We evaluated the imaging capability of murine Tc-99m-labeled antimelanoma Fab fragments in 12 patients with clinical stage II and III melanoma. Tc-99m-NRX118.7 antimelanoma Fab fragment, 10.0 to 27.2 mCi (370-1, 006 MBq), was injected IV 30 min after irrelevant nonspecific intact antibody and 5 min after intact specific antibody were given. In all patients, whole-body scans and spot views were obtained. Single photon emission computed tomography (SPECT) was additionally performed in eight of the patients. The procedure was well tolerated, and 31 of 38 known foci of melanoma were detected (sensitivity, 82%). SPECT aided in detecting and better localizing lesions in the head, neck, and chest. The specificity of the technique was satisfactory when interpretation was performed with a knowledge of normal sites of accretion and excretion of technetium-99m activity such as the kidneys and gut. In several instances, lesions were discovered by means of the antibody scan before detection by other methods, and in two instances, the lack of visualization on antibody scan of a palpable mass correctly indicated that no melanoma was present in the mass. Scan results in three patients led to alterations in patient care; including preventing aggressive surgical and nonsurgical treatments. Although these data are encouraging, evaluation in additional patients will be essential to determine the clinical utility of this antibody scan in the management of patients with melanoma.