5-(3-(3-[(123)I]iodoallyloxy)phenyl)-10,15,20-tris-(3-carboxymethoxyphenyl)porphyrin ([ (123)I]2) was prepared for biologic evaluation in a B16-F10 tumor model to examine its potential as an imaging agent. The I-123-labeled porphyrin [(123)I]2 was purified by reverse-phase high-performance liquid chromatography (HPLC) to give a decay-corrected radiochemical yield of 8%-13% (n=9) and the radiochemical purity after HPLC purification was >95% and the overall radiolabeling time was 160 minutes. The in vitro cell uptake of [ (123)I]2 increased with time. Biodistribution in mice bearing the B16-F10 tumor, after an intravenous injection of [(123)I]2, also showed a time-dependent accumulation of the porphyrin in tumor tissue (10.35 %ID/g at 6 hours). The tumor-to-muscle ratio was 3.49, 3.38, 3.07, and 3.13 at 1, 2, 6, and 24 hours, respectively. The gamma-camera images of (123)I-porphyrin demonstrated a high focal accumulation of radioactivity in the B16-F10 melanoma tumor.