The biodistribution studies showed the primary uptake to be in liver and kidneys, the organs of excretion and metabolism. The uptake observed on dapt secretase with administration of excess nonradioactive ligand showed a trend suggesting some specific binding in the liver and kidney. However, the differences were not statistically significant and may be related to changes in blood flow or excretion rate caused by the larger mass dose. The high uptake in liver may reduce the utility of the radioligand for imaging studies of metastatic colon cancer in the liver, but the resolution of current PET scanners should minimize the effect of very high liver uptake on the ability to observe other adjacent organs. Unfortunately, the lack of demonstration of specific binding in the in vitro tissue dipping experiments in rat testes suggests the need for a more selective and less lipophilic compound. However, final judgment will require evaluation in an animal model that expresses high levels of the A3AR receptor in a tissue that lacks a tissue–blood barrier.