The invention provides a pharmaceutical agent delivery composition comprising: (i) a transport polymer comprising a linear or branched peptide having from about 10 to about 300 amino acid residues, having from about 5 to 100% histidine residues, and optionally having from 0 to about 95% non-histidine amino acid residues; (ii) at least one pharmaceutical agent; and optionally (iii) one or more intracellular delivery components in association with the transport polymer. The invention also provides methods for using such composition to deliver the pharmaceutical agent to the interior of cells.