Single chains of the collagen-model polypeptide with sequence (Pro-Pro-Gly)(10), hereafter referred to as (PPG)(10), aggregate to form rod-shaped triple helices. Precipitation diagrams of (PPG)(10) as a function of pH and various molecular mass poly(ethylene glycol) concentrations have been measured. These results were used to design experiments to test the quality of (PPG)(10) crystal grown on ground (in gelled and free solutions) and in space in two different facilities, the Advanced Protein Crystallization Facility based on the free-interface diffusion technique and the Granada Crystallization Facility based on counter-diffusion technique. Experiments were monitored by optical microscopy on earth. X-ray diffraction analysis of the grown crystals reveals the benefit of the counter-diffusion technique. (C) 2008 Elsevier B.V. All rights reserved.