Actively　targeting　probe　1b,　an　unsymmetrical　bivalent　dipeptide　mimic,　selectively　bound　melanoma　over　healthy　skin　tissue　in　histological　samples　from　patients　and　Sinclair　swine.　Modifications　to　1b　gave　agents　2-4　that　contain　a　near-IR　aza-BODIPY　fluor.　Contrary　to　our　expectations,　symmetrical　probe　3　gave　the　highest　melanoma-to-healthy　skin　selectivity　in　histochemistry　and　experiments　with　live　cells;　this　was　surprising　because　2,　not　3,　is　unsymmetrical　like　the　original　lead　1.　Optical　imaging　of　3　in　a　mouse　melanoma　model　failed　to　show　tumor　accumulation　in　vivo,　but　the　probe　did　selectively　accumulate　in　the　tumor　(some　in　lung　and　less　in　the　liver)　as　proven　by　analysis　of　the　organs　post　mortem.