Blends of poly(epsilon-caprolactone) as the matrix material and 1, 2, 4, or 8 wt.-% of a polypeptide were prepared by dissolution in a cosolvent and coprecipitation into cold methanol. A low- and a high-molecular-weight poly(gamma-benzyl L-glutamate), a poly(gamma-methyl L-glutamate) and a poly(D,L-phenylalanine) were used as reinforcing components and compared with a liquid-crystalline (LC) polyester derived from a double-substituted terephthalic acid. Films of all blends were subjected to stress-strain measurements. A weak reinforcing effect was found for the poly(gamma-benzyl L-glutamate)s, a somewhat stronger influence for the other polypeptides and the strongest effet for the LC-polyesters 1.