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Drug-targeting strategies can increase the efficacy and reduce the side effects and toxicity of conventional chemotherapy or may lead to new radiolabeled molecules useful for diagnosis and therapy. To identify and characterize new carrier molecules, we evaluated a peptide that had been identified by phage display technology.The peptide p160 (VPWMEPAYQRFL) was prepared by solid-phase peptide synthesis and radiolabeled with (125)I or (131)I. The radiolabeled peptide and derivatives of it were used to study binding and internalization in vitro and to assess their distribution in tumor-bearing mice.Cell-binding assays on the human neuroblastoma cell line WAC 2 indicated the affinity and specificity of (125)I-labeled p160 toward neuroblastoma cells. Binding of the (125)I-labeled p160 was inhibited up to 95% by the unlabeled peptide. Furthermore, 50% of the total bound activity was internalized into the neuroblastoma cells. Biodistribution studies on nude mice showed a higher tracer accumulation in tumors than in most organs. Perfusion of the animals reduced uptake in all tissues, whereas tumor uptake remained constant. Fluorescence-activated cell-sorting studies with fluorescein isothiocyanate-labeled p160 demonstrated an increased fluorescence signal. Investigation of the binding properties of the fragments p160-8-1, p160-8-2, and p160-8-3 indicated that the sequence EPAYQR might be of significance for the binding of p160.These data indicate that the p160 peptide is an attractive candidate for the development of a neuroblastoma-specific vector that can be used for drug targeting or radiopeptide-based diagnosis and therapy.