The effects of mono-, di-and trivalent ions on the rheological properties of a purified mucus glycoprotein gel have been investigated. Monovalent ions increased the fluidity of the gels in a concentration dependent manner. The effect of calcium was pH dependent; at neutral pH values this ion produced a maximum in the gel viscoelasticity at a concentration of 0.5 mM, whilst at pH 5.0 the increase in viscoelasticity was sustained up to 3.0 mM. The same concentrations of copper (II) at pH 5.0 had a similar but greater effect on the viscoelasticity. Al 3+ at pH 3.0 increased the viscoelastic moduli throughout the range studied (0.1–2.0 mM), whereas iron made the gels more fluid at low concentrations, but increased the viscoelasticity to above control values at a concentration of 2.0 mM.