Localization of malignant melanoma using monoclonal antibodies. Finding a screening test to evaluate patients with cancer for occult metastatic disease, as well as imaging all known disease, is a goal of research efforts. Twenty-nine evaluable patients with deeply invasive (stage I), regional nodal (stage II), or systemic (stage III) melanoma underwent imaging by administration of a preparation of the antimelanoma antibody labeled with technetium 99m. Scan results indicated that 28 of 32 confirmed metastatic sites were imaged with this technique (88% sensitivity). Analysis of the individual positive sites revealed that nodal basins and visceral metastases accounted for the highest percentage of metastatic sites imaged, with 14 (88%) of 16 nodal basin metastases and all four visceral metastases being detected through imaging. Occult nodal disease was detected in the iliac nodal chain in two of the 29 patients. The imaging of benign tumors and nodal basins not containing disease accounted for a confirmed false-positive rate of 21%. Three (10%) of the 29 scan results were confirmed to be false-negative. In vivo tumor localization with monoclonal antibodies showed a sensitivity similar to that of other roentgenographic procedures for identifying metastatic disease and was useful in two of three patients in identifying occult iliac nodal disease, a region that is difficult to evaluate with physical examination and other imaging modalities. 