Peptide-based drugs are now viable alternatives to biopharmaceuticals, such as antibodies. Most of the past limitations of peptides have been removed by new technologies, so that peptides now face similar hurdles to antibodies. Phage-display technology provides novel peptides that bind protein targets with high affinity and specificity. Most marketed peptide-based drugs are receptor agonists derived from natural peptides. To address the need for antagonists, novel strategies have been developed for inhibiting receptor-ligand interactions. We review results from phage display in finding peptide drug candidates and conclude with some business benefits of developing peptides.