The use of the blood-brain barrier and of tumor-specific antibodies to concentrate boron selectively in gliomas for neutron capture therapy is considered experimentally and theoretically. The time-dependent concentration of two anionic boranes, B₁₂H₁₁SH^2––and B₁₂H₁₁ SOSB₁₂H₁₁^4––, in the blood, brain, and tumor of rats bearing a tumor of gliomatous origin is reported. The rate of clearance of each anionic borane from the blood is correlated with the fraction of non-protein bound anion in the plasma. The use of antibodies to carry therapeutically useful amounts of boron to tumor-specific or tumor-associated antigens on the tumor cell surface will require different numbers of boron atoms bound per antibody depending on several immunological and physical parameters. Calculations using published values of antibody-antigen association constants and of cell surface antigen densities predict that in order to obtain 10 μg ¹⁰B/g tumor from 10 to over 10,000 boron-10 atoms will have to be bound per tumor antigenic site.