The present invention concerns fusion of Fc domains with biologically active peptides and a process for preparing pharmaceutical agents using biologically active peptides. In this invention, pharmacologically active compounds are prepared by selecting a peptide that modulates the activity of a protein of interest and preparing a pharmacologic agent having an Fc domain covalently linked to the peptide. Linkage to the Fc domain increases the half-life of the peptide, which otherwise would be quickly degraded in vivo. The peptide can be selected, for example, by phage display, E. coli display, ribosome display, RNA-peptide screening, yeast-based screening, chemical-peptide screening, rational design, or protein structural analysis.