The effects of a simple salt (1:1 electrolyte, KCl) on the calcium alginate gel formation and the gel stability of alginates varying in molecular weight and mannuronate/uluronate (M/G) ratio were investigated by an equilibrium dialysis technique. There was no significant dependence of the calcium binding capacity among the alginates. However. the G residues exhibited a stronger affinity for Ca2+ than M residues. The addition of a simple salt to the dialysis solution resulted in displacement of bound Ca2+ and swelling of the calcium alginate gel that increased with concentration of the simple salt. Even the Ca2+ bound with the G block was displaced by monovalent cations at high salt concentration.