[Cu-61] diacetyl-bis(N-4-methylthiosemicarbazone) ([Cu-61]ATSM) was prepared using in house-made diacetyl-bis(N-4-methylthiosemicarbazone) (ATSM) ligand and [Cu-61]CuCl2 produced via the Zn-nat(p, x)Cu-61 (180 mu A proton irradiation, 22 MeV, 3.2 h) and purified by a ion chromatography method. [Cu-61]ATSM radiochemical purity was > 98 %, as shown by HPLC and RTLC methods. [Cu-61]ATSM was administered into normal and tumor bearing rodents for up to 210 minutes, followed by biodistribution and co-incidence imaging studies. Significant tumor/non-tumor accumulation was observed either by animal sacrification or imaging. [Cu-61]ATSM is a positron emission tomography (PET) radiotracer for tumor hypoxia imaging.