The recent hypothesis that counteranion-mediated dynamic inversion of charge and solubility might contribute to diverse functions of oligoarginines in biomembranes was tested with two fluorescently labelled oligomers, FL-R8, one of the most active cell-penetrating peptides, and its longer version, FL-R16. We report evidence for counteranion-mediated phase transfer from water into bulk chloroform and anionic lipid-bilayer membranes as well as reverse-phase transfer from bulk chloroform and across intact lipid-bilayer membranes into water. The differences found between FL-R8 and FL-R16 with regard to location in the bilayer and reverse-phase transfer from bulk and lipid-bilayer membranes into water implied that the reported results may be relevant for biological function.