New Tc-99m radiopharmaceuticals with the ligand (o-hydroxyphenyl)diphenylphosphine have been prepared and their biodistributions evaluated in rats. The monoxo Tc(V) complex [ 9 9 m Tc(O)Cl(PO) 2 ], the Tc(IV) complex [ 9 9 m Tc(OH) 2 (PO) 2 ], the Tc(III) complex [ 9 9 m Tc(PO) 3 ], and the nitrido Tc(V) complex [ 9 9 m Tc(N)(PO) 2 ] have been characterized by TLC and HPLC chromatography, and their chemical structure elucidated by comparison with the corresponding complexes obtained using the β-emitting isotope Tc-99g. Biodistribution studies of these complexes have been carried out in rats.