We will use SANS to investigate the nanoscopic structure – i.e., sizes in the range 2-200 nm – of complexes formed by cell-penetrating peptides and nucleic acid species. The hierarchical structure spans a wide range of lengthscales and a wide q range is required. Contrast variation in H2O/D2O will be performed to isolate scattering from the peptide and nucleic acid components in the complexes between so-called Trojan peptides and plasmid DNA. The Trojan peptides to be employed include the Tat-HIV segment GRKKRRQRRRPPQ and Penetratin sequence RQIKIWFQNRRMKWKK.