[en] The symmetrical complexes [^99mTc][TcN(R₂PS₂)₂] [R = CH₃, CH₂CH₃, CH₂CH₂CH₃, CH₂(CH₃)₂], and the unsymmetrical complex [^99mTc][TcN(Me₂PS₂)(Et₂PS₂)] have been prepared, at tracer level, through a two-step procedure involving the preliminary formation of a prereduced technetium nitrido intermediate followed by substitution reaction onto this species by the appropriate dithiophosphinate ligand [R₂PS₂]Na. The chemical identity of the resulting complexes have been established by comparison with the corresponding ⁹⁹Tc-analogs prepared, at macroscopic level, by reacting the complex [⁹⁹TcNCl₄] [n-Bu₄N] (n-Bu = n-butyl) with an excess of ligand in methanol, and characterized by elemental analyses and spectroscopic techniques. The complexes are neutral and lipophilic, and possess a square pyramidal geometry, with an apical Tc N group and two dithiophosphinate ligands spanning the four positions on the basal plane through the four sulfur atoms of the >PS₂ group. In vitro studies showed that these radiopharmaceuticals are stable in solution and that their chemical identity was not altered after incubation with rat blood. Biodistribution studies have been carried out in rats and primates. The results demonstrate that these compounds are significantly retained into the brain of these animals for a prolonged time. Planar gamma camera images have been obtained in monkeys showing a good visualization of the cerebral region. However, the existence of persistent blood activity yields a brain/blood ratio lower than that observed with other ^99mTc-based brain perfusion imaging agents