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The gastrin-releasing peptide receptor (GRPR) is overexpressed on a variety of carcinomas and has been the target for detection and treatment of these neoplasms in animals. In particular, analogues of the tetradecapeptide bombesin (BN) have been radiolabeled with ^99mTc and ¹¹¹In for detection of GRPR-positive tumors by gamma ray scintigraphy. The goal of this study was to evaluate the potential of the bombesin analogue, DOTA-Aoc-BN(7−14), for positron-emission tomographic (PET) imaging after radiolabeling with the positron-emitter ⁶⁴Cu. A saturation binding assay on PC-3 human prostate cancer cells showed that ⁶⁴Cu-DOTA-Aoc-BN(7−14) had an equilibrium binding constant (Kd) of 6.1 ± 2.5 nM and a receptor concentration (Bmax) of 2.7 ± 0.6 × 10⁵ receptors/cell. The radiolabeled analogue also showed rapid internalization with 18.2% internalized into 10⁵ PC-3 cells by 2 h. The tumor localization of ⁶⁴Cu-DOTA-Aoc-BN(7−14) was 5.5% injected dose per gram in athymic nude mice bearing PC-3 xenografts at 2 h postinjection. The tumor retention with respect to the 2 h value was 76% and 45% at 4 and 24 h, respectively, and was GRPR-mediated as shown by inhibition with a coinjection of excess peptide. MicroPET imaging of ⁶⁴Cu-DOTA-Aoc-BN(7−14) in athymic nude mice bearing subcutaneous PC-3 tumors showed good tumor localization. Further studies with ⁶⁴Cu-pyruvaldehyde-bis(N⁴-methylthiosemicarbazone) (⁶⁴Cu-PTSM) suggested that low blood flow to the PC-3 tumors may have limited the localization of ⁶⁴Cu-DOTA-Aoc-BN(7−14). This study demonstrates that ⁶⁴Cu-DOTA-Aoc-BN(7−14) can be used to detect GRPR-positive tumors by PET imaging.