The influence of salt impurities on foaming of N-methyldiethanolamine (MDEA) solutions was studied. Studies of the influence of individual ions on foaming of fresh MDEA solution showed that Ca2+, Fe2+, Mg2+, and Sr2+ tended to induce foaming and stabilize the foam. The effects of the cations followed the order Fe2+ > Sr2+ > Mg2+ > Ca2+. The anions F-, CH3COO-, HCOO-, Cl-, Br-, SO4 (2-), C2O4 (2-), S2O3 (2-), and SCN- exerted a slight inhibitory effect on foaming. The order of the tendency to induce foaming changed to Sr2+ > Mg2+ > Fe2+ > Ca2+ if these ions were present simultaneously in the solution. Ca2+ enhanced significantly the tendency to induce foaming but had no effect on the foam stability. Fe2+ and Sr2+ had a synergic effect on the tendency to induce foaming and stabilize the foam.