Single crystals of (Pro-Pro-Gly)₁₀ were grown by the hanging drop method. The crystals diffracted to a resolution of 1.8 Å. In the crystals the polypeptides form triple helices that aggregate end-to-end mediated by the solvent molecules, with the basic repeat being 20 Å along the helical axis. Analysis of the 20 Å structure of (Pro-Pro-Gly)₁₀ using data up to a resolution of 1.9 Å revealed that the overall structure is in accordance with the 7/2 model proposed for collagen. The three strands are held together by the (Gly) N-H…O (Pro-X) hydrogen bond interactions, and additional stability is provided by the (Pro-Y) C^α -H…O (Pro-X) hydrogen bonding interactions.