An attenuated oncolytic Edmonston (Ed) strain of measles virus encoding the human thyroidal sodium iodide symporter (MV-NIS) with potential gene expression and antineoplastic activities. After attachment to and fusion with host tumor cell membranes, MV-NIS may induce tumor cell syncytia and tumor cell lysis. When combined with iodine 123 (I-123), expressed NIS facilitates uptake of I-123 by MV-NIS-infected tumor cells, allowing noninvasive imaging of these cells. MV-NIS may also enhance the oncolytic activity of MV against radiosensitive tumor cells by facilitating the uptake of iodine 131 (I-131) by MV-NIS-infected cells. The cellular receptor for MV is the human CD46 antigen, a type 1 integral membrane glycoprotein found on nearly all human tissues and overexpressed on many cancer cell types.