We report a study of seven children with recurrent stage IV neuroblastoma comparing the uptake pattern of 123I-metaiodobenzylguanidine (mIBG) with 99mTc-labeled monoclonal antibody (MAb) BW 575 by the tumor lesions. Immunofluorescence studies of bone marrow had verified specific binding of the antibody to the tumor cells. The majority of tumor sites was detected both by mIBG and MAb scans. However, five of 26 lesions were not detected by mIBG and eight of 26 were false negative by immunoscintigraphy. The false negative lesions by mIBG belonged to five different patients (one of five primary, four of five bone marrow). In conclusion, MAb BW 575 may detect mIBG-negative neuroblastoma sites. The presence of antibody-negative sites suggests the utilization of both scintigraphy methods together.