Elastin-like polypeptides (ELPs) are pentapeptide oligomers that aggregate when heated above a critical temperature that is determined by the specific sequence of amino acids in the monomer. Meyer and Chilkoti have made use of this phenomenon to develop a strategy for the temperature-dependent purification of ELP-tagged recombinant proteins (see p. 1112). Their new system provides an inexpensive and simple alternative to chromatography-based purification schemes.