The lipid bilayer, which comprises all cell membranes, represents a formidable barrier to the delivery of large hydrophilic molecules into cells. The ability to introduce information-rich molecules into cells is a challenge in the development of new therapeutics for diseases not currently amenable to small molecule intervention. This work focuses on the delivery of peptide-based molecules including; inhibitors, substrates and carriers into cells. A series of peptide-based inhibitors against caspase-3, an intracellular enzyme involved in apoptosis, were assessed for their cell membrane...