This page is designed for searching peptides with a desired frequency of functional amino acids, such as charged, polar, and hydrophobic residues. You may select a frequency range for a functional amino acid. For example, if you wish to find all cell-penetrating peptides containing more than four aliphatic residues, you may set the minimum value for aliphatic to 4. The output frequency table can be sorted based on the frequency of any functional amino acid. For more information, see the HELP page.