Pluronics P94 are block-copolymer showing prolonged circulation time and tumor-cell internalization in vitro, suggesting a potential for tumor accumulation and as a drug carrier. Here we report the results of the radiolabeled-P94 unimers (P94-111In-DTPA) on tumor uptake/retention and biodistribution after intravenous and intratumoral injection to tumor-bearing mice. Intravenous administration results in a high radioactive signal in the liver; while in tumor and other healthy tissues only low levels of radioactivity could be measured. In contrast, the intratumoral injection of P94 resulted in elevated levels of radioactivity in the tumor and low levels in other organs, including the liver. Independently from the injection route, the tumor tissue presented long retention of radioactivity. The minimal involvement of off-target tissues of P94, together with the excellent tracer retention over-time in the tumor designates Pluronic P94 copolymer as a highly promising carrier for anti-tumor drugs.@en