We have used our ability to control β-peptide secondary structure in order to explore the effects of conformational stability and geometry of guanidinium display on cell entry. Both of these factors affect the rate and relative amount of β-peptide accumulation in the cytoplasm and nucleus of live HeLa cells. These β-peptides do not show significant differences in cell surface binding, implying that structure and guanidinium display are important in a later step in cell entry than initial surface binding.