62Cu labeled diacetyl-bis(N4-methylthiosemicarbazone) (62Cu-ATSM) has been proposed as a generator-produced, positron-emitting tracer for hypoxic tissue imaging. From basic studies, the retention mechanism of 62Cu-ATSM is considered to be closely related to cytosolic/microsomal bioreduction, a possible system for hypoxic bioreductive drug activation. In order to evaluate the characteristics of 62Cu-ATSM, PET studies were performed in 4 normal subjects and 6 patients with lung cancer. 62Cu-ATSM cleared rapidly from the blood with little lung uptake (0.43+/-0.09, uptake ratio; divided by the arterial input function) in normal subjects. Intense tumor uptake of 62Cu-ATSM was observed in all patients with lung cancer (3.00+/-1.50). A negative correlation was observed between blood flow and flow-normalized 62Cu-ATSM uptake in three of four patients. In contrast, 62Cu-ATSM uptake was not related to that of 18F-fluorodeoxyglucose. The negative correlation between blood flow and flow normalized 62Cu-ATSM uptake suggests an enhancement of retention of 62Cu-ATSM by low flow. 62Cu-ATSM is a promising PET tracer for tumor imaging, which might bring new information for chemotherapeutic treatment as well as radiotherapy of hypoxic tumors.