Imaging of two reporter genes in the same mouse. A nude mouse carrying two tumors (left, dopamine 2 receptor [D2R]; right, herpes simplex virus type 1 thymidine kinase [HSV1-tk]) was imaged in a microPET system with tail-vein injection of ~ 250 μCi [18F]-fluoroethylspiperone (FESP) and, 24 hours later, with ~ 250 μCi 8-[18F]-fluoropenciclovir (FPCV). Imaging began 1 hour after injection of each tracer. These results show the ability to image both the D2R and the HSV1-tk reporter genes in the same living mouse with microPET. The scale represents the accumulation of FESP and FPCV measured as percent injected dose per gram of tissue (%ID/g).