A radioimmunoconjugate containing the murine IgG1 anti-CD45 monoclonal antibody (MoAb) BC8 labeled with the gamma-emitting isotope indium 111 (In 111), with potential radioimaging application. Upon administration, indium In 111 anti-CD45 monoclonal antibody BC8 binds to CD45 antigen, a receptor protein tyrosine phosphatase expressed on the surface of most of the normal and malignant hematopoietic cells. After binding and internalization by CD45-expressing tumor cells, radioactive In 111 allows for the detection of BC8 distribution and tumor localization using gamma scintigraphy.