Calcification of implant or surrounding tissues represents an important complication of its function. The role of the molecular structure of a model hydrogel on the calcification is studied here in a simple in vitro, cell free system. The results show that-COO- containing polymers have an inhibitory effect on Ca2+ crystal formation. This process seems to be unspecific, because the polymers of different structure and origin have an inhibitory effect. However, its efficiency is related to a different extent of Ca2+ binding capacity of distinct polymers.