Zinc pigments react in aqueous alkaline media (e.g., water-borne paints) by the evolution of hydrogen. Low molecular weight styrene-maleic acid and styrene-acrylic acid/styrene-acrylate copolymers can inhibit this corrosion reaction of zinc pigments in a mixture of water and butyl glycol in the ratio 9 : 1 at a pH value of 10 (ammonia). High molecular weight styrene-maleic acid copolymers are only very poor corrosion inhibitors. This was proved by volumetric measurement of the evolved hydrogen. There seems to be a correlation between the content of carboxyl groups of the low molecular weight styrene-maleic acid and styrene-acrylic acid/styrene-acrylate copolymers and the evolved hydrogen volume in ammoniacal aqueous medium : The lower the acid number of the styrene copolymers, the lower is the evolved hydrogen volume. Low molecular weight styrene copolymers neutralized with dimethylethanolamine inhibit the corrosion reaction much better than with ammonia.