AbstractThe new ligands 1,6‐dimethoxy‐3,4‐hexanedione dioxime (DMHD) and 1,6‐diethoxy‐3,4‐hexanedione dioxime (DEHD) were synthesized and their boron containing99Tc/99mTc complexes, formed by reduction of pertechnetate with BH4‐, were isolated, purified and characterized by IR/UV/VIS spectroscopy and FAB mass spectrometry. These rather stable cationic complexes differ significantly in lipophilicity as assessed by their octanol/saline partition coefficients and HPLC capacity factors. Unexpectedly the organ uptake and clearance of both complexes in mice proved to be very similar with only the uptake of99mTc‐DMHD in the kidneys