Vasculature targeting agents have been tested as cancer therapeutics for the past few years. Such therapy could be accomplished using, for example, bifunctional (two-domain) peptides. RGD-4C-GG-D (KLAKLAK) 2 , a peptide designed by Ellerby and coworkers (1999) (full sequence: ACD-CRGDCFCGGKLAKLAKKLAKLAK), binds selectively to α V β 3 integrin receptors expressed in tumor neovasculature and, after internalization, effectively induces apoptosis of endothelial cells. The aim of this study was to examine if RGD-4C-GG-D (KLAKLAK) 2 would efficiently target cells, among them B16(F10), that overexpress α V β 3 receptors, and whether it would be suitable for therapeutic treatment of primary B16(F10) murine melanoma tumors. Thus, the peptide would target two distinct tumor compartments: that formed by endothelium of blood vessels and that made up of neoplastic cells. The therapeutic peptide was recognized and did induce apoptosis in B16(F10) cell line. Tumor growth inhibition was observed following direct intratumoral administration. However, cessation of peptide administration led to rapid tumor growth and death of the animals.