Abstract Since 201Tl is widely used in SPECT and porphyrins are important biological carriers, we tried to obtain a stable complex between thallium and porphyrins. The thallium porphyrin complex was synthesized by reaction of 201Tl(III) with porphyrin at 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin (H2PFPP) for 60 min at 100°C. The complex was analysed via TLC and HPLC stability (in the final formulation and human serum) and the partition coefficient of the complex was determined. The biodistribution of the labeled compound in vital organs of wild-type rats was investigated. The complex was prepared with high radiochemical purity (> 99% ITLC, > 99% HPLC, specific activity: 13–14 GBq/mmol) (log P = 1.92). The stability of the Tl+3-complex seems to be low since the complex or free thallium is rapidly cleared through the kidneys and the liver.