Abstract New cationic 99Tc/ 99mTc complexes formed with various symmetrical and asymmetrical vicinal dioximes of different carbon chain length (C 5–C 8) were synthesized by reduction of pertechnetate with BH 4 −, separated by HPLC and characterized by i.r./u.v./vis. spectroscopy, FAB mass spectrometry and electrophoresis. All complexes studied are trisdioximes containing boron as a constituent. Their lipophilicity, as assessed by the octanol/saline partition coefficient, ranges over almost four orders of magnitude. The myocardial uptake of the 99mTc complexes in mice proves to be lower than expected. The organ distributions are distinctly affected by the lipophilicity, the position of the dioxime group and the introduction of a terminal methoxy group.