Recurrent prostate cancer presents a challenge to conventional treatment, particularly so to address micrometastatic and small-volume disease. Use of α-radionuclide therapy is considered as a highly effective treatment in such applications due to the shorter range and exquisite cytotoxicity of α-particles as compared with β-particles. 213Bi is considered an α-emitter with high clinical potential, due to its short half-life (45.6 minutes) being well matched for use in peptide-receptor radionuclide α-therapy; however, there is limited knowledge available within this context of use. In this study, two novel 213Bi-labeled peptides, DOTA-PEG4-bombesin (DOTA-PESIN) and DO3A-CH 2CO-8-aminooctanoyl-Q-W-A-V-G-H-L-M-NH2 (AMBA), were compared with 177Lu (β-emitter)-labeled DOTA-PESIN in a human androgen-independent prostate carcinoma xenograft model (PC-3 tumor). Animals were injected with 177Lu-DOTA-PESIN, 213Bi-DOTA-PESIN, or 213Bi-AMBA to determine the maximum tolerated dose (MTD), biodistribution, and dosimetry of each agent; controls were left untreated or were given nonradioactive 175Lu-DOTA-PESIN. The MTD of 213Bi-DOTA-PESIN and 213Bi-AMBA was 25 MBq (0.68 mCi) whereas 177Lu-DOTA-PESIN showed an MTD of 112 MBq (3 mCi). At these dose levels, 213Bi-DOTA-PESIN and 213Bi-AMBA were significantly more effective than 177Lu-DOTA-PESIN. At the same time, 177Lu-DOTA-PESIN showed minimal, 213Bi-DOTA-PESIN slight, and 213Bi-AMBA marked kidney damage 20 to 30 weeks posttreatment. These preclinical data indicate that a-therapy with 213Bi-DOTA-PESIN or 213Bi-AMBA is more efficacious than β-therapy. Furthermore, 213Bi-DOTA-PESIN has a better safety profile than 213Bi-AMBA, and represents a possible new approach for use in peptide-receptor radionuclide α-therapy treating. recurrent prostate cancer.