The growth of calcium carbonate crystals has attracted growing attention as a model system for biomineralisation processes. Organic molecules and gelatinous matrices are known to play an essential role in the formation of hard tissues. For the investigation of the function of specific influence factors, a model experiment is necessary. Several hydrogels were previously tested as growth matrices for calcium carbonate. For laboratory experiments, a double diffusion set-up for the growth of crystals in gels was established earlier. Calcium carbonate crystals were grown in polyacrylamide hydrogels. Here the influence of the polymer content in the hydrogels on the crystallisation behaviour is reported. Time-resolved and spatially resolved crystallisation experiments were conducted. The collected calcium carbonate precipitates were analysed by light microscopy, scanning electron microscopy and X-ray diffraction. The morphology of the developing crystals was found to be dependent on the polymer content of the hydrogels. (c) 2008 Elsevier B.V. All rights reserved.