In an effort to develop new, clinically useful 99Tcm-diaminodithiol (99Tcm-DADT) complexes for the evaluation of regional cerebral perfusion, basic diaminodithiols (DADT-TM, DADT-HM and DADT-MHM) and three diaminodithiol ligands functionalized with p-iodophenethyl (DADT-IPE), N-ethyl-p-fluorophenethyl amine (DADT-EFPE) or N-ethyl-p-iodophenethyl amine (DADT-EIPE), whose chemical structures are analogous to N-isopropyl-p-iodoamphetamine (IMP), were synthesized, labelled with 99Tcm and evaluated comparatively in experimental animals. In addition, the relationships between the chemical properties of the derivatives and their brain uptake and retention were investigated. The results were: (1) Isomeric configuration of 99Tcm-DADT complexes has an influence on uptake and retention in the rat brain. (2) In basic 99Tcm-DADT complexes, a correlation exists between initial brain uptake and lipophilicity, but in 99Tcm-DADT complexes containing a chemical structure similar to that of IMP, no correlation exists. (3) 99Tcm-DADT-IPE has relatively high uptake and long retention in the rat brain.